Zotero Maps: Visualizing Archaeology?

You can now map your Zotero Library:

Potential Use Cases:
Map Your Collection By Key Places:
Many records from library catalogs and journal databases come pre-loaded with geographic keywords. Zotero Maps lets you quickly see the relationships between the terms catalogers, authors, and publishers have assigned to the items in your collection. Similarly, as you apply your own geographic tags to items you can then explore those geographic relationships. Whether you’re looking at key locations in studies of avian flu, ethnographic work in the American southwest, or the history of the transatlantic slave trade, the tags associated with your items provide valuable geographic information.

Map Places of Publication:
In many cases places of publication include crucial information about your items. If your working on a project involving the history of the book, how different media outlets cover an issue, or how different journals present distinct scientific points of view, the places in which those items are published can provide valuable insight.

In 2007, I was trying something along these lines using Platial (now deceased). Now – since you can add objects from things like Opencontext.org into your Zotero library, and describe these using tags, you could begin to build a map of not only ‘things’ but also the relevant reports etc, all from your browser, without doing any of the fancy coding stuff…

From my library:

World War II, Google Earth, and the South Etruria Survey

The British School at Rome’s celebrated ‘South Etruria Survey’, conducted by the School in the 1950s to the 1970s was partly in response to the rebuilding of Italy in the wake of World War II. As a research assistant on the BSR’s Tiber Valley Project in the late 1990s, I was helping to re-evaluate the SES. We would examine the original files & maps, unpack the original finds crates, and enter all of it into a GIS. The results from the restudy are still coming out.

How I wish we’d had something like Google Earth! Google has just added imagery from World War II to Google Earth. We did have access to the original military maps of the region, and aerial photographs, but what I love about Google’s implementation is the sliding ‘clock’ bar. Watch how a zone has changed over time… So the connection with the SES – some of the Google material overlaps the study region; hopefully more is to come…

Digital Humanities Summer Institute at U Vic 2010

The offerings at the Digital Humanities Summer Institute at the University of Victoria (BC) are quite interesting this year – though I note nothing on Agent Modelling.  If I was in that neck of the woods, I’d be quite keen to take the following –

Geographical Information Systems in the Digital Humanities

Ian GregoryThe course offers an introduction to the theory and practice of using Geographical Information Systems (GIS) to research the past. It will be primarily based on using the ArcGIS software package, the use of Google Earth to disseminate humanities data will also be explored. The course will be relevant to historians, historical geographers, demographers, and others with an interest in the geographies of the past. Quantitative and qualitative approaches will both be explored. We would welcome attendees bringing their own data so that we can explore how to get it into GIS form and what can then be done with it.

There are scholarships and some other limited financial aide available.

Dynamic Modeling in a GIS Environment Autumn 2009

Courtesy of Andrew Crooks GIS and Agent Modelling blog , I learn today of a series of seminars exploring the latest in GIS & dynamic modelling, at the Global GIS Academy

Of particular interest (to me, at any rate) are the following:

October 28th

Ling Bian (Buffalo)
A dynamic social network model for disease transmission

The work in this presentation was sponsored by a health care agency and some of the results reported remain confidential until we have permission from that agency to make the presentation available.

See also: Bian, L. (2003) The representation of the environment in the context of individual-based modeling. Ecological Modelling, 159 (2-3): 279-296.

Bian L 2004 A conceptual framework for an individual-based spatially explicit epidemiological model. Environment and Planning B 31(3): 381-95. @ www.envplan.com/abstract.cgi?id=b2833

Bian, L., Liebner, D. (2004) A network model for dispersion of communicable diseases . Transactions in GIS , 11(2): 155-173. @ www3.interscience.wiley.com/journal/118490206/issue

November 18th

Raja Sengupta (McGill)
What’s so spatial about Agent-Based Models?

Download PDF (3.1 Mb) of presentation

See also: Sengupta, R., and Bennett, D.A.(2003) Agent-based modeling environment for spatial decision support. International Journal of Geographical Information Science, 17(1): 157-80

Sengupta, R., Sieber, R. (2007) Geospatial Agents, Agents Everywhere…. Transactions in GIS, 11(4): 483-506.

Derek Karessenberg (Utrecht)
Integrating spatio-temporal GIS data with spatio-temporal models.

Download PDF (1.3 Mb) of presentation HERE (ITEM 4)

See also: Karssenberg, D., Schmitz, O., de Vries, L.M., and de Jong, K (2008) A tool for construction of stochastic spatio-temporal models assimilated with observational data. 11th AGILE International Conference on Geographic Information Science 2008, University of Girona, Spain. 7 pages

Seminars on GIS & Archaeology

seen over at Stoa.org

Contemporary Roles for Spatial Analysis in Archaeology

The UCL Institute of Archaeology Seminar Series (January–March 2010)
31-34 Gordon Square, London WC1H 0PY
Mondays 4pm, Room 612 (followed by a wine reception)


11 January 2010 – Benjamin Ducke (Oxford Archaeology)
‘Science without software no longer. Archaeological data analysis and the Open Source paradigm’

18 January 2010 – Chris Green (University of Leicester)
‘Temporal GIS and archaeology’

25 January 2010 – Tony Wilkinson (Durham University)
‘From household to region: incorporating agency into the interpretation of regional settlement’

1 February 2010 – Tim Williams (University College London)
‘Earth viewers and GIS in archaeological resource management: access and accessibility’

8 February 2010 – Luke Premo (Max Planck Institute for Evolutionary
‘A spatially explicit model of Early Stone Age archaeological landscapes’

15 February 2010 (Reading Week – no seminar)

22 February 2010 – Frederic Fol Leymarie (Goldsmiths College)
‘Advances in 3D procedural modelling with applications to archaeology’

1 March 2010 – Michael Barton (Arizona State University)
‘Stories of the past or science of the future? Archaeology and computational social science’

8 March 2010 – Irmela Herzog (Archaeological Heritage Management of the Rhineland)
‘Patterns of movement, least cost paths and our understanding of the archaeological record’

15 March 2010 – Kate Devlin (Goldsmiths College)
‘Illuminating virtual reconstructions of past environments’

22 March 2010 – Mark Lake (University College London)
‘Rewind and fast‐forward: how archaeological GIS analyses recapitulate general theory’

I know Luke Premo and Mark Lake have both been doing ABM work; maybe somebody could record these lectures and post them somewhere… I’m still in no danger of being anywhere near London.

I’ve been reading around historians’ use of GIS lately; I think the archaeologists are far in the lead – but there’s still the problem of moving from using GIS to recognise patterns to using GIS to explain the patterns it seems to me.

Of course, I’m happy to be wrong on that.

TravellerSim: Growing Settlement Structures and Territories with Agent-Based Modeling: full text

Below follows the full text of my and James’ TravellerSim article. Why leave it to sit on a shelf somewhere, when a random google search might find it, and find it useful?

2008 (with J. Steiner)  “Travellersim: Growing Settlement Structures and Territories with Agent-Based Modelling” in Jeffrey T. Clark and Emily M. Hagemeister (eds) Digital Discovery: Exploring New Frontiers in Human Heritage. CAA 2006. Computer Applications and Quantitative Methods in Archaeology. Proceedings of the 34th Conference, Fargo, United States, April 2006. Budapest: Archaeolingua.


TravellerSim: Growing Settlement Structures and Territories with Agent-Based Modeling

Shawn Graham1 , James Steiner2

1Department of Classics

University of Manitoba

Winnipeg, Manitoba, Canada


2 Turtlezero.com

Agent-Based Modeling Consultancy

Philadelphia, Pennsylvania, USA


Agent-based modeling presents the opportunity to study phenomena such as the emergence of territories from the perspective of individuals. We present a tool for growing networks of socially-connected settlement structures from distribution map data, using an agent-based model authored in the Netlogo programming language, version 3.1.2. The networks may then be analyzed using social-networks analyzes tools to identify individual sites important on various network-analytic grounds, and at another level, territories of similarly connected settlements. We present two case studies to assess the validity of the tool: Geometric Greece and Protohistoric Central Italy.

1   Introduction

This paper presents a tool that uses agent modeling to simulate the actions of individual travellers in a given region, who set out from sites known through archaeological field survey. Territories and site hierarchies are thus grown from the dynamics of the model, rather than imposed from above by the archaeologist. In our approach we use social networks analysis to investigate the resulting structure(s) in order to identify and predict overlapping territories of similarly connected settlements, and settlements whose positioning in the networks holds implications for the overall social importance of those settlements. The agent-based model is a re-implementation and re-imagination of an entropy-maximizing gravity settlement model built by Tracey Rihll and Andrew Wilson (1991). Certain archaeological patterns seem to agree with the results of the social networks analysis and the simulation, pointing to the validity of the tool. This is one of the first studies in the Greco-Roman world to use agent-based modeling in this fashion (see also Graham 2006a, 2005a), and so the results necessarily are tentative; however we feel that as a model and a tool TravellerSim holds great promise for understanding and predicting site interactions and by extension, territories. This work follows in the tradition of research carried out by Kohler 1995, Kohler et al. 2005; Doran et al. 1994; and Cherry 1977. We turn first to discuss the foundations and implementation of the agent model,1 then we will consider the validity and some preliminary analysis of the results and their implications for the emergence of territories and leading settlements in a region.

1.1 Polygons, landscapes, and networks

The Thiessen polygon has had a chequered service in archaeology since its introduction in the 1960s and 1970s. As a technique for indicating a likely territory around a site or settlement (however defined), its advantage lies in its simplicity. One connects lines at right angles to a connecting line drawn between adjacent sites, to form a polygon. The assumption is that places nearer to a site will likely enjoy a greater amount of interaction than sites further afield (DeMers 2000:305-307). Given the complexity of human interactions (with other humans, and with geography and landscape), the Thiessen polygon has been criticized for its simplicity (e.g., Haselgrove 1986). Yet it continues to enjoy a certain currency (e.g., Dytchowskyj et al. 2005; Fulminante 2005), no doubt due to the ability of modern geographic information systems to generate the polygons at the click of a mouse.

Considering the problems of the Thiessen polygon is useful however in that it forces one to think about the complexities of defining a territory. The context of a territory, the setting for the human and physical interrelationships that make up various overlapping territories (of commerce, of family, of extraction, of farming etc.), is the wider landscape. The landscape architect Anne Whiston Spirn reminds us that the context of landscape is ‘process.’ She points out that the word ‘context’ has an active, Latin root: ‘contexere’, to weave. She writes:

Context weaves patterns of events, materials, forms, and spaces….A river, flowing, is context for water, sand, fish, and fishermen; flooding and ebbing, it shapes bars, banks, and valley. A gate is context for passage, its form determining how things flow through it: narrow gates constrict; gates of screens block large things and permit smaller ones to pass through. Context is a place where processes happen, a setting of dynamic relationships, not a collection of static features.

[Spirn 1998:133. emphasis added].

If that is correct, then territory is one set of dynamic relationships interleaved with another set of dynamic relationships. This is an understanding very similar to recent work by Julian Thomas on landscape. He argues that “…the challenge of working with landscape is one of holding these elements [facets of landscape] in a productive tension rather than hoping to find a resolution” (Thomas 2001:166). One way to hold those elements in Thomas’ ‘productive tension’ would be to weave them together into a network geography. The urban geographers Massey, Allen, and Pyle conceive the interrelationships within and between settlements of all sizes to be a vast network of overlapping and intersecting ties, corresponding to different worlds of experience where every settlement is a node of social relationships in time and space, in multiple overlapping and intersecting networks (Massey et al. 1999:100-136). That is to say, the same place may belong in different ‘orbits’ around other settlements simultaneously, depending on the actions of individuals who somehow belong to that place. The problem then becomes two-fold. How do we stitch settlements together into a network? And having done that, how do we extract anything meaningful from that tangled web?

Our answer to both questions is, with agent-based models and social network analysis. With an agent-based model, we generate a network of interrelationships mediated through individuals. With social network analysis, we untangle that network to produce meanings for us as archaeologists that are ‘produced in the dynamic working of the relationships between people, things, and places’ (Thomas 2001:180). In this way we move from ‘dots-on-a-map’ to understanding something of the human interrelationships between sites.

1.2 Agent-based models, individualism, and rules

One of us (Graham) has elsewhere discussed what agent-based models are, and where they fit into wider theoretical programs (Graham 2006:55-54); here we will recap that argument. Our aim with TravellerSim was to grow networks of interconnected settlements through individual agency. Agent-based modeling, also known as individual-based modeling (Gilbert and Troitzsch 2005:172-216; Gimblett 2002:5) is explicitly concerned with individual actions. This should not be equated with systems approaches, which try to describe the entire complexity of the society in question by modeling subsystems (Aldenderfer 1998:91-120). The emphasis in systems theory was on equilibrium, and the interrelationships between components were known (or presumed to be known). However, the advent of chaos and complexity theories demonstrated that this is not the case for the vast majority of natural or social phenomena: the interrelationships are not well known (or not even possibly able to be known), they are unstable, and they are non-linear (Aldenderfer 1998:104; Cilliers 1998; Lewin 1993). In this case, the investigator should not be concerned with describing global characteristics, for these emerge from the interactions of individuals. In the words of John Barrett (2001:155) “the social totality should not form the basic domain or unit of archaeological study…as individuals learn so they make society [emphasis in original]”. It is individual learning or decision making that is the hallmark of the agent-based model.

In an agent-based model, individuals are simulated as autonomous pieces of software which are allowed to interact with each other and their environment. Each agent is its own bounded heterogeneous object – although every agent may have the same suite of variables, the combination of values for each agent is unique. The agents are given simple rules of behavior drawn from whatever phenomenon we wish to study. How the rules are implemented by each individual agent depends on its combination of characteristics, and by its situation vis-à-vis its local environment and neighboring agents. From all of these interactions, an artificial society begins to emerge. Indeed, while in this particular model the emphasis is on the individual, other levels of society can be modeled and allowed to interact with and upon the individuals’ from whose actions those levels have emerged.

The problem of developing the rule-sets, of encoding the relevant aspect of social behavior, is not insignificant. How does one reduce the complexity of social interaction to a mathematical function?  Generally, the simpler the rules, the easier it is to verify and to validate model results, and for the model results to have a wider applicability. While it is entirely possible to encode extremely complicated rules, it becomes correspondingly more difficult to show that any emergent behavior is not simply an artifact of the coding. For that reason we prefer instead to keep our rules as simple as possible, and have them correspond with general principals of behavior. The important thing for a designer is not to become fixated on the process of assigning a numerical value. Rather, what we want to do is design a rule that is broad enough to allow a range of behaviors and yet is narrow enough not to admit every possible behavior (Agar 2003: 4.16-4.18). We want to design a certain ‘phase-space’ that matches what we believe to be true of our subject. The numbers themselves are only significant in that they allow a certain range of behaviors. Agent-based modeling forces us to formalize our thoughts about the phenomenon under consideration. In order to encode the behavior, we have to be specific about what we think, and why we think that way.

2 Implementing TravellerSim

TravellerSim’s methodological underpinnings are built on the gravity-settlement model developed by Tracey Rihll and Andrew Wilson (1991). Rihll and Wilson were concerned to explore the emergence of the Classical poleis of Greece from the earlier Geometric Period. They developed a model which asked,

When the poleis were coming into existence, did discrete communities align themselves with those with whom they had most in common – those with whom they experienced the most intense interaction? Did location vis-à-vis other settlements have a significant effect on their affiliation and union? [Rihll and Wilson 1991:60]

In contrast to many archaeological investigations of territoriality and landscape, they considered the question of ‘situation’ rather than ‘site.’ That is, they consider the human positioning of a site, rather than its physical setting. In their model, a distribution of sites from the Geometric represents a starting point for simulating ‘credits’ and ‘debits’ of interaction from site to site. Mathematically, their model attempts to solve a series of differential equations, eventually settling on the ‘best’ answer. Two parameters, aside from the 2-dimensional scatter of settlements, are also modeled, to simulate difficulties in communications and the benefit of concentrated resources (hence attractiveness of a site for interaction).

Rihll and Wilson’s basic hypotheses are that:

1) interaction between any two places is proportional to the size of the origin zone and the importance and distance from the origin zone of all other sites in the survey area, which compete as destination zones;

2) the importance of a place is proportional to the interaction it attracts from other places

3) the size of a place is proportional to its importance

(Rihll and Wilson 1991:60-63)

It is worth noting that these three hypotheses necessarily create feedback loops. In this model, it is not strictly essential to know much about the sites in question. Indeed, Rihll and Wilson found that it worked best when no assumptions whatsoever were made about a site’s a priori importance (1991:70). This simplifies the computing and modeling considerably, since all that is necessary as a model input is a distribution map of contemporaneous sites. Their model does appear to predict eventual settlements of some importance, as well as indicating the hierarchy of lesser sites that ‘look’ to the main one.

2.1 How the model works

Rihll and Wilson’s original model could be described in a single equation. Moreover, Rihll and Wilson’s model describes a global, current state for the entire region under consideration, and all interactions are calculated at the same time. While it might be possible to create an agent model that follows their algorithm exactly, when we considered the problem from the point of view of an individual, we recognised that no individual would ever have such knowledge. At most, they might know something about their home place, and the state of places in their local neighborhood. The key then to translating their model into an agent framework lies in the verbal rather than the mathematical description of their three hypotheses, with two important alterations in the first hypothesis:

1) interaction between any two places is proportional to the size of the place the agent is currently at, and the importance and distance from that place to places within a day’s travel, which compete as destination zones

Our model therefore has two ‘breeds’ of agents: settlements, and travellers. It is helpful to think of the settlement agent as a ‘genius loci’, or spirit of the place. Each traveller has a limited vision, or knowledge of its neighborhood. The ‘vision’ is set variable around 20 km or roughly the distance covered in a day’s travel by foot (see Duncan-Jones 1990:7-29 on travel times in the Greco-Roman world). Each traveller compares the attractiveness of three potential destinations within their range of vision, choosing to travel to the most attractive site. Attractiveness is calculated according to a localised version of Rihll and Wilson’s equations (i.e., only three sites, rather than all sites simultaneously). The calculation is based on the settlement’s importance, number of visitors it has hosted, and the distance to the settlement. Two user-controlled modifiers are also used in the calculation: the benefit of concentrated resources, and the difficulty of communications. These two parameters allow the user to alter the travellers’ environment, simulating more difficult travel conditions (winter for instance) or magnify the benefits to be found in a settlement (initially, every settlement starts with the same level of importance). Having each traveller select from three potential destinations would seem to be an arbitrary limitation. This is partly a programming short-cut, and partly a reflection of an agent’s limited knowledge of the world. In terms of programming, if every agent were to calculate attractiveness for every destination, the simulation would consume enormous resources to make the calculations. Since each traveller does its own localised computations, and since there can be more than one traveller facing out (and hence having different settlements in its range of vision) in the initial time-step of the simulation from each settlement, the overall effect is for attractiveness to be calculated for all of the settlements on a given map in the time it takes for an agent to pick one destination from amongst three. (We plan in later versions of this simulation to have agents’ select one site from all of the destinations within their range of vision). The traveller then sets off, leaving a coloured trace behind it, indicating where it has travelled.

Translated into pseudo-code the first hypothesis looks like this:

let destination1 be one-of (settlements within-my-range-of vision)

let destination2 be one-of (settlements within-my-range-of vision) with [self != destination1]

let destination3 be one-of (settlements within-my-range-of vision) with [self != destination1 and self != destination2]

let score be benefit-of-concentrated-resources vs. distance-to-destination(1,2,3) considered-against importance-of-destination(1,2,3)

set travel-goal destination-with highest-score

Netlogo (Wilensky 1999) is written in what may be called ‘near-English.’ In the pseudo-code above, ‘highest-score’ for instance is the name for a sub-procedure which compares the scores of the three potential destinations within what this agent considers to be a day’s travel (its ‘vision’, how far it can see of its world).

The next two hypotheses can be translated into code in much the same way. The settlements are both two-dimensional points in space, and active agents aware of their environment. Their primary function is accounting, keeping track of interaction. When a traveller arrives at a settlement, the settlement increases its importance. The traveller tells the settlement where the traveller has originated from (its ‘home settlement’), and the settlement also gets a boost in its importance by virtue of this ‘reflected glory.’ If a settlement does not attract any visitors in a given turn, its importance declines. (By ‘reflected glory’ we mean a settlement’s importance is in part a reflection of the places to which it is connected – a visitor from a small village does little to enhance the status of a major place; but a visitor from a major place can enhance the importance of a small village).

By considering the question from the point of view of the individual traveller, we have transformed Rihll and Wilson’s systems-theory approach into a complex systems approach.

2.2 Model outputs

The computing was run on an AMD Athlon XP 2400+ desktop computer, with 2.00 GHz and 512 MB of RAM.

This model produces various data which can be considered on their own or exported into another program for analyzes. Figure 1 is a screen-shot of the model interface window. Parameter controls are on the left, the map window is in the centre, and the output controls are on the right. The ‘territories’ histogram in the top right of the interface window merely counts the number of settlements by color. The number of unique colors (as reported by the histogram) corresponds with the number of unique, local, territories (which may also be seen on the map).


Figure 1. Screen-shot of the model interface window, showing outputs after a typical model run. In the central window is the distribution map of settlements from the protohistoric period in Central Italy. Different maps may be loaded into the model; the model reads the scale bar and adjusts accordingly. The network as represented in the interface window is not the network of connected settlements, rather it is the tracing of all of the travellers’ wanderings (a traveller that leaves settlement A and eventually gets to settlement Z creates a direct social connection between A and Z, so the graph of socially-connected settlements is different from the actual wanderings of travellers). Travellers change their color to match that of the settlement they are at, if it is more important that the settlement they have left. In this fashion, from an initial state where every settlement has its own unique color, ‘influence’ of one settlement over another may be visualised. The histogram at the top right counts the number of unique colors. Settlements also reset their size in proportion to their importance compared against the most important settlement, providing another visual clue to a settlement’s importance as the simulation progresses.

The ‘write network’ button asks all of the settlements to list the settlements-of-origin for visitors to that settlement. This list is the social network of the settlements, which is not the same as the pattern of interconnections displayed in the view window. All travellers remember their home settlement (‘settlement-of-origin); by visiting a new site, they create a social connection between it and their home site. Therefore, by comparing the settlement social network with the paths of the travellers, we already have different levels of social complexity emerging from the model, where the colored traces left by the travellers indicate a local geography, while the social network corresponds to a global geography.

Social Network Analysis. While both these levels could be analyzed on social network grounds, we are more interested in the global network of interconnected settlements. The local level is mediated through geographical proximity, where connections are made as the traveller looks in the immediate neighborhood for another settlement to visit. At the global level, travellers begin to tie otherwise geographically disparate settlements together through their own personal agency (see Graham 2006b:25 for an example of personal agency warping local geography in the Sabina region of Central Italy). By running the model through numerous iterations, we develop a statistical picture of how individuals create a regional geography of interconnected sites. Each model run is analyzed using social network analysis tools; we then consider which settlements and structures occur most often to be our ‘emergent’ settlement structures.

Social network analysis2 has its foundations in the mathematics of graph theory, which considers sets of connected objects. It is predicated on the idea that overall network shape affects both the options open to individuals (connections facilitate action, absence of connections prohibit actions), and how a particular society as a whole behaves (see Graham 2006c on social networks in the central Italian brick industry).

The social network of interconnected settlements, generated by travelling individuals (the global level), can be studied from multiple viewpoints to meet Thomas’ idea of the ‘productive tension’, the resolution of his two understandings of the word ‘landscape’, of ‘a territory which can be apprehended visually’, and a ‘set of relationships between people and places which provide the context for everyday conduct.’ Social network analysis allows us to consider both local and global positioning of a settlement vis-à-vis every other settlement.

The network approach necessarily assumes that the network under consideration is static, representing a particular moment-in-time (but on evolving networks, see Barabàsi 2002; Barabàsi and Albert 1999). In each iteration of the model considered here, we ran the simulation for thirty simulated days-worth of travel. With SNA, we can analyze the ties between the settlements, in order to determine amongst other things which settlement is better connected to the others (and so in a position of social power), which settlement forms a link between otherwise disconnected clumps of settlements (and so forming a social bridge), or for studying how clumps of individual settlements connect to ever-wider social groupings (group dynamics). Based on their positioning within a network, with regard to other settlements, one can determine which actor would wield the most influence over others, or manage the most information flow. This is an approach which has been used successfully in terms of ancient history for prosopographical and geographical studies, where the implied linkages between actors have been some sort of real-world foundation (Müller 2002; Duling 1999; Remus 1996; Clark 1992; Kendall 1971). We can also analyze which settlements are allied in their patterning of interconnections, and then use that patterning to determine likely global ‘territories’, and to understand the interrelationships of those territories.

Social network analysis is a powerful tool for untangling the web of relationships amongst actors. It may be objected that we are only analysing an artifact of our own construction. We are reasonably confident however that our two-fold approach is valid, based on the results of two geographic case studies. First we will consider the output for geometric Greece, and then the output for protohistoric central Italy. Then, we will show how this model may be used for untangling localised relationships by considering the distribution of Republican farm sites in the middle Tiber Valley.

Of a number of different network metrics (see Hanneman and Riddle 2005), the following seemed to be useful on archaeological terms:

Fragmentation: This Keyplayer metric measures the effect of cutting the network into isolated components (a component is a set of mutually connected nodes). The metric identifies ten nodes the removal of which would cause the maximum of fragmentation. In archaeological terms, these would be settlements that form junctures between otherwise isolated areas.

Power: This Ucinet metric examines the network to identify nodes that sit at the head of locally isolated networks. It is similar to fragmentation, but differs in the patterning of the interconnections within components. Nodes identified by this metric are well-connected to poorly-connected other nodes. That is, they depend on these ‘powerful’ nodes for access to the wider network.

Flow Betweeness: This Ucinet metric looks at every possible path between every possible pair of nodes. The nodes which appear most often on these paths are the nodes through which the most information flows. This is obviously a computationally-intense algorithm. Settlements identified by this metric could be assumed to be very important for the transmission of culture, for the economy, and so on.

Degree: This is the simplest metric, and is calculated by the model itself. It is simply the count of connections, with the settlements with the greatest number ranking highest. The assumption here is that places that are well-connected are likely to be richer, bigger, and so more important.

Certain nodes or settlements will likely appear in more than one metric. These are settlements which we would suggest should receive more attention from archaeologists. Finally, the network analysis can be used to identify territories by looking for factions within the patterning of connections. This Ucinet metric looks at the network to identify sets of nodes with similar patterns of interconnections, which it labels a ‘faction.’ It can also identify, by looking at the densities of overlap between factions, which factions would be likely ‘allied’ and which would have little contact. There is no particular reason in the operation of the model why these factions when plotted should be geographically contiguous; that they are geographically-discrete indicates a certain level of validity in the method.

3   Model results and validity

It is our intention to go into greater detail about our model results in a later publication. Here, we will discuss what our early results are indicating, the degree to which we think we can trust these results, and where we intend to explore our data further in the future. Our purpose here is not to explore the complete ‘phase-space’ (possible results given all possible combinations of the variables) but rather to verify that the model is doing what we set out to have it do.

3.1 Caveats

We used the emergence of the Classical poleis as our benchmark for determining whether the model was valid or not. This allowed us to compare our results with the original results by Rihll and Wilson. If our re-implementation of their model hypothesis in a completely different modeling paradigm produced similar results, then we could feel reasonably certain that the hypothesis did indeed capture something essential about the interaction of settlements. Moreover, our subsequent analysis of the social network (a step not contemplated by Rihll and Wilson) would be grounded on data in some sense ‘from the real world’, although computer-generated. Being able to produce social network data from the model represents an extension from Rihll and Wilson’s original model.

There is of course a great deal of mathematics going on as this model runs. However, for understanding what the model does, these mathematics are not the most important consideration. Rather, the greater import lies in the description of how the individual agents (both travellers and settlements) interact. If we get the description right of what an individual agent may do in our simulation, then any emergent result must have some validity.

It is worth stating that we were unable to tune the model (adjusting the parameters) to obtain a desired result: we could not ‘fiddle the numbers’ so that Athens was always consigned to the bottom rank of settlements, for instance. Knowing however that Athens did become a major settlement, we could use that information as a guide – if we found settings where Athens would emerge somewhere in the top quarter of settlements according to the power metric (our benchmark metric), we considered that to be a reasonably valid model run.

We ran the simulation on each map with settings as described below, for 30 iterations each time. Then, we exported the resulting network of socially connected sites to Ucinet and analysed it against our chosen metrics. Finally, we ranked the settlements by the number of times they emerged as most important in the various metrics. It is worth noting that, if we were interested in one settlement in particular, the way it scored in the different metrics could be used to characterise its ‘role’ in this simulated world (with attendant implications for its role in the real world of the time).

3.2 Central Greece

We ran the model on the same data as Rihll and Wilson’s original model. In all of the model runs discussed hereafter, our settings for ‘difficulty of communications’ and ‘benefit-of-concentrated-resources’ were set to mimic a relatively difficult area to move across, but also a bit of a boost to the attractiveness of sites. They were in the same range of settings that Rihll and Wilson found best produced results in their model which made historical sense (“benefit of concentrated resources” = 1.025; “difficulty of communications” = 0.25”; a further parameter not in the Rihll and Wilson model, “number of travellers per site” was set at three making 324 travellers over 108 sites. The model was run initially using a random seed so that we could explore the effects of the two main parameters; thereafter we ran it 50 times on each map, at the two settings mentioned above. We also made no assumptions about the relative importance of sites, and so set every site’s initial importance to exactly the same level.


Figure 2. Distribution map of Geometric-era settlements in Central Greece.

This area under consideration (Figure 2) eventually evolved into the city-states and regions of Attica, the Argolid, the Thebaid, and the Isthmia. Our model clearly shows a similar differentiation. While not every later classical city of prominence emerged from our model, enough of them did to suggest that the model is on the right track. It clearly indicated Corinth, Athens, and Megara as locally important sites. The most important site, according to our model, was not a city at all but rather the site which became in time the extra-urban sanctuary of the Argive Heraion. This is a particularly intriguing result, given the arguments advanced by De Polignac in Cults, Territory and the Origins of the Greek State (1995). There, the argument is that originally in Greek culture the concept of ‘territory’ was a religious idea, not a political one. He identifies the role of urban and rural sanctuaries as being the twin poles of an axis around which the community revolved. The ‘sacred way’ between these two poles was often monumentalised through paving or architecture, thereby being a ‘reification’ of the religious festivals and processions through which the community defined itself to itself, and its connection to particular parcels of land. By this argument then the Heraion of Argos and its relationship to Argos was more typical of the development of the ‘polis’ than Athens. Athens was without any major extra-urban sanctuary, and so is an anomaly amongst the Greek cities; it is only a historical accident that we pay so much attention to Athens the atypical case. In our model, we used the presence/absence of Athens as one of the indicators of a good model run, and all the same the Heraion of Argos emerged as more important. This congruence between our model and the arguments of De Polignac would seem to reinforce the validity of our model and the three hypothesis of Rihll and Wilson.

The relative positioning of a settlement, vis-à-vis every other settlement, is clearly a very important factor in the evolution and emergence of important places – human situation versus physical site. At the higher level of ‘territories’, the model seems to accurately predict the location and extent of allied groupings. The patterning of densities within the factions also points to a heightened importance for Corinth and the Isthmia (the patterning of ‘alliances’ seems to lead to this faction in particular), which we would have already suspected for this period on the evidence of pottery manufacture and export (viz. the dominance of Corinthian wares in the Archaic period).

3.3 Central Italy

We then ran the model on data from the protohistoric period (roughly, the 10th to 8th centuries AD) of Central Italy (Figure 3, a base map amalgamated from Cifani 2003:149-150, Smith 1996:240, Potter 1979:54), with the same settings as before (this time, at three travellers per settlement, there were 285 travellers total). Here, the model indicated Falerii Veteres, Fidenae, and Veii as being extremely important settlements, which agrees with what we would have expected from Roman history (Figure 4 depicts the state of the simulation at the end of the model run). It is interesting also that these settlements – all early conquests of Rome – ranked higher than Rome did itself in the model runs. Rome’s early expansion in the historic period is cast by this simulation as a series of wars to re-jig its positioning within the social networks. Rome appears in a faction with Veii and Fidenae (who were alternately at war and at peace with Rome from an early date) and other settlements south of the Tiber in the region of Latium (Figure 5, Figure 6). This faction generated by the model corresponds almost exactly with Latium vetus, the original territory of the Latin people (a significant archaeological characteristic at this time being miniaturised funerary goods included in cremation burials (Bietti Sestieri and De Santis 2000:23)). Falerii Veteres (the last of these to be conquered by Rome) sits in another faction altogether. According to the Factions analysis, the pattern of interconnections also puts the Falerii Veteres faction in the most central location possible. Geographically, this is the area along the Treia River and its confluence with the Tiber. Interestingly, Falerii Veteres supported Fidenae and Veii against Rome in the early wars (Livy 4.17-18, 21; 5.8-24)(Haynes 2000:211).  We intend to explore these data and their implications more fully in a future publication.


Figure 3. Protohistoric sites in Central Italy


Figure 4. Simulation output. Benefit of concentrated resources = 1.025. Difficulty of communications = 0.25. 30 iterations. The display routines within the model seem to indicate five different ‘territories’.


Figure 5. Mapping of the results of the factions analysis on the model run. F1 – ‘coastal’ faction; F2 – Praeneste faction; F3 – Rome faction; F4 – Falerii Veteres faction; F5 – ‘upper’ faction; F6 – Umbrian faction. Arrows indicate direction of the relationship, ie F1 ‘looks to’ F5 and F4.


Figure 6 depicts the same information as Figure 9, but as a pure network graph. 95 settlements can be grouped into 6 factions.

The Tiber Valley. Since the model seemed to produce results which make sense over a large area, we were curious to see if it could be used to understand settlement interconnections in a small area. We ran it against survey data from the British School at Rome’s Tiber Valley project (Patterson and Millett 1998). The BSR kindly provided data on over 2000 sites known from surface survey. We extracted the sites identified as “villa’ sites and ‘farm’ sites, from the Republican period, which brought the number down to a more manageable 361 sites within a roughly 25 by 25 km square  (Figure 7). For these runs, we adjusted the average vision parameter to be variable around 5 km, on the assumption that the daily needs of farming could be met within this distance. Having three travellers per settlement on this map created over 1000 agents (which significantly slowed down the simulation). We ran the model first on ‘farm’ sites, then on ‘villa’ sites.

What we were hoping was that the model would be able to demarcate ‘farming regions.’ None of these sites has been excavated, and so our conclusions here are very tentative. However, the top ten sites that the analysis suggested were ‘powerful’ should merit further investigation (which we hope to do in a future publication). What is interesting is the pattern of interactions between the factions (due to the density of connections created by the model, the factions analysis took about nine hours to complete). Amongst the villa factions (Figure 8), there is a strong directionality towards Rome (which would be situated towards the bottom of the diagram). Amongst the farms, the directionality seems focused on the centre of the region (Figure 9). This patterning of factions is suggestive of later patterns of landholding known from brick production in the same area. Brick production in the first century often employed stamps which carried the name of the estate on which they were produced (see Graham 2005b, 2006b:55-72). While archaeometric studies have not yet pin-pointed production locales, the patterning of use of stamped brick within the Valley does allow us to speculate. In particular, certain factions which emerge from the distribution of farm sites seem to overlap with a number of later sites using brick from the estates of the brothers Tullus and Lucullus Domitius. An estate of theirs is known to have existed in the region near Bomarzo (Graham 2006b:56). Perhaps what the faction analysis is suggesting is not so much that ‘here are the ancestral lands of the Domitii’, but rather despite changing title to land, continuities exist in the parcelling out of the land over time. Another ‘farming faction’ seems to overlap with the Falerii Veteres faction from the central Italian map as well.


Figure 7. ‘Farm’ sites in the Tiber Valley.


Figure 8. Graph of the factions analysis on ‘villa’ sites. The graph is arranged in more-or-less geographic position, with sites near Rome being at the bottom in Faction 4. Faction 1 and Faction 5 are across the Tiber in the Sabina region. Contrast this graph with the maps of the ‘economic geography’ of the Tiber Valley in Graham 2005b: 117-120.


Figure 9. Graph of the factions analysis on ‘farm’ sites. Sites near Rome are again at the bottom, in Faction 5.

4   Conclusion

With Travellersim, we have developed a tool which may be used against distribution maps at a variety of scales. This tool should help investigators generate social networks with a good degree of validity in terms of the actual historical/geographical patterns of communications, but of course, given the caveats above, the complete phase space of the model should be explored when using it in a formal study. These social networks can then be studied in turn to identify, at one level, sites important on various network-analysis grounds, and at another, territories of similarly connected settlements. The model’s programming is relatively accessible and simple to follow, and unlike many computer simulations it may be ‘tinkered with’ at ease.  It is also grounded firmly in archaeological theory.

The original model created by Tracey Rihll and Andrew Wilson considered three hypotheses about how settlements interacted – that interaction was proportional to the size of places; that importance of places was proportional to the interaction attracted from other places; and that the size of a place was proportional to its importance.  We were intrigued by their results, which did seem to predict the emergence of later Classical city-states from the patterning of settlements in the preceding Geometric period.  However, we wanted to frame the hypotheses from the point of view of an individual. Why do individuals travel, and what are the consequences for the emergence of territories from those individual decisions to travel to particular places? Agent-based modeling methodologies allowed us to recast the Rihll and Wilson model into a framework which appeals to us archaeologically because it is predicated on the interactions of individuals and their environment.  It is also object-oriented; other investigators may be interested to extend the model by adding more variables or objects to the set-destination routine (for instance) to allow decision making based on simulated kinship groups. Travellers might be modeled to be more inclined to travel to places where others from their ‘home settlements’ have already travelled. Personal relationships mediated the interactions between the city states of Classical Greece and in the later Roman period and it is certainly desirable to incorporate those dynamics in elaborations of the model. However, we feel that in this first instance the limitations placed on the current model are justified given the kind of data that went into it to begin with: simple distribution maps of sites from particular eras.

The initial results of our model runs produce results very similar to those found by Rihll and Wilson for Greece. Indeed, the emergence (in our model) of the Argive Heraion as the most important site directs our attention to the important role of extra-urban sanctuaries in state formation in the Greek world, an argument that De Polignac made from a completely different approach. The results for Italy suggested a new way of looking at the emergence of Rome, while the results from the Tiber Valley point to a new approach for drawing meanings from intensive survey data. While these results are not conclusive, they do suggest that our model (and its underlying hypotheses) has a degree of real-world validity and it therefore may be of use to other investigators. We expect that when we are able to correlate the suggested most important sites (according to the various network metrics) against the material culture gathered in field survey, we will be able to demonstrate fully the validity of the model. In any event, TravellerSim demonstrates the potential for agent-based modeling, with its grounding in individual agency, to be transformative for the practice of archaeology. We present TravellerSim as a tool for that purpose. For the full potential of this tool to be useful, we invite investigators to break it, find its flaws, dispute its assumptions, and develop something better.


We would like to thank the University of Manitoba and the Canada Research Chair in Roman Archaeology, Lea Stirling, for supporting this research. We are also grateful to the British School at Rome, and the Centre for Modeling Complexity at Mesa State College, Grand Junction Colorado. Finally, we would like to thank the participants at the CAA 2006 for their perceptive comments on this paper, and the comments of the anonymous reviewers. Any shortcomings are of course our own fault.


1 All program code may be downloaded from http://home.cc.umanitoba.ca/~grahams/Travellersim.html (Graham and Steiner 2006). The base maps considered in this paper are also provided as sample data in the model. It is our hope that other researchers might use, alter, improve and extend our model for their own investigations.

2We use Keyplayer and Ucinet, available from Analytictech.com (Borgatti et al.1999).

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Historical Maps, GIS, and Second Life

I’ve just come across a presentation (in three parts) given by David Rumsey, over a year ago. Worth a view!

“A talk given by David Rumsey at the March 6, 2008 launch of his historical map library and exhibition in the virtual world of Second Life. The talk was delivered at the Rumsey Map Islands in Second Life. All of the maps in the talk can also be seen and downloaded from Rumsey’s free online map library at www.davidrumsey.com

Part I

Part II

Part III

10th VAST International Symposium on Virtual Reality, Archeology and Cultural Heritage

First call for papers:

10th VAST International Symposium on Virtual Reality, Archeology and Cultural Heritage
7th Eurographics Workshop on Graphics and Cultural Heritage


September 22-25, 2009, Valletta, Malta


Call for Papers

-Towards a “digital agenda” for the integration of technologies into Archeology and Cultural Heritage-

Nearly every organization whose mission includes promoting access to cultural information, is well aware of the value of digital applications, and digital technologies are finding their way into cultural organizations. Nevertheless, a clear-cut division still exists between humanities researchers, computer science researchers, information scientists, librarians, and campus technologists, which prevents a complete achievement of the  potential represented by the integration of these disciplines. Each community has distinctive practices, lingo, assumptions, and concerns. Understanding technology needs of the humanities, and more specifically of Archaeology, Libraries and Cultural Heritage, has particular relevance to the future of knowledge and education delivery, as well as, to develop shared technology services to enhance humanities research now and in the future.

The main goal of this VAST is to bring together professionals from all fields to start a true dialogue on CH needs and ICT solutions and achieve a true integration of disciplines. This VAST aims at disseminating the idea of a more systematic integration of digital practices in research and education programs for CH, exploring good practices, guidelines and skills development possibilities to structure long-term initiatives and move towards a “digital agenda” for Archaeology, Libraries and CH.

This is why we are seeking contributions that advance the state of the art in the technologies available to support sustainability of human heritage.

– 2/3/4D Data Capture and Processing in CH
– Augmentation of physical collections with digital presentations
– Data Acquisition Technologies
– Digital Libraries
– Digital capture and annotation of intangible heritage (performance, audio, dance, oral)
– Interactive Environments and Applications for CH
– Long term preservation of digital artefacts
– Metadata, classification schema, ontologies and semantic processing
– Multilingual applications, tools and systems for CH
– Multimedia Data Acquisition, Management and Archiving
– Multi-modal interfaces and rendering for CH
– On-site and remotely sensed data collection
– Professional and Ethical Guidelines
– Serious games in CH
– Standards and Documentation
– Storytelling and Design of Heritage Communications
– Tools for Education and Training in CH
– Usability, Effectiveness and Interface Design for CH Applications
– Visualization

Archeology: Dr Zahi Hawass – General Secretary of the Supreme Council of Antiquities of Egypt
Museums: Mme. Christiane Naffah – Director of the Research and Restoration Center for France Museums

The best papers presented at VAST 2009 will be selected for re-submission on a special edition of the upcoming ACM Journal on Computing and Cultural Heritage (JOCCH), an online, peer reviewed publication.

VAST 2009 introduces the “VAST-STate-of-the-Art Reports (VAST-STARs)”, inspired by the EG STARs. These are papers providing useful novel overviews of research in the fields of computer graphics, computer science  and related fields that can benefit the multidisciplinary nature of VAST. They are survey papers in what the community considers important areas that have not been covered before or recently. Their aim is to give a detailed account of the principles, algorithms and open problems of a research area, so that an interested reader can quickly become up to speed in this field.  We warmly encourage all colleagues to submit to the VAST-STARs reports. The VAST-STARs will be published with the full papers and are also eligible for the best paper award. Two VAST-STARs will be selected by peer review and will be published in the EG proceedings together with the full papers.  VAST-STARs authors will present their work with a 60 minute presentation during VAST 2009.

We are soliciting five types of contributions:

=Full research papers presenting new innovative results. These papers will be published by Eurographics in a high-quality proceedings volume.

=VAST-STARs providing a useful novel overview of research in the fields of computer graphics, computer science  and related fields that can benefit the multidisciplinary nature of VAST.

=Project papers focusing on on-going projects, the description of project organization, use of technology, and lesson learned not innovative technical content. These papers will have an oral presentation and will be included in a “Projects & Short Papers” proceedings volume. Authors will have the option to present a poster during the breaks to provide more information regarding the project.

=Short papers presenting preliminary ideas and works-in-progress. These papers will have an oral presentation and will be published in the “Projects & Short Papers” proceedings volume.

=Tutorials and Workshops: half-day and full-day working sessions that provide an opportunity to educate and share on key topics of interest face-to-face. Tutorial submissions will be published in the “Projects & Short Papers” proceedings volume. Workshops that provide supplemental materials in time for the CD-ROM printing will also be included. All material will be made available on the VAST 2009 website.

All types of submissions will be reviewed and feedback given to the authors. See detailed information on the VAST 2009 website under Submissions.

Event Committee: Kurt Debattista – University of Warwick, Sandro Spina – University of Malta
Program Committee: Cinzia Perlingieri – University of California at Berkeley, Denis Pitzalis – The Cyprus Institute, STARC
Local Organisational Committee: Sandro Spina – University of Malta, Chris Porter – University of Malta, Keith Bugeja – University of Warwick.
VAST-STARs Committee: Fotis Liarokapis (Coventry University – UK), Michael Ashley – University of California at Berkeley

– ISC –
Achille Felicetti (PIN – University of Florence)
Aderito Marcos (Universidade do Minho – Portugal)
Alan Chalmers (University of Warwick – UK)
Alan Smeaton (Dublin City University – Ireland)
Alberto Proenca (Universidade do Minho – Portugal)
Daniel Pletinckx (Visual Dimension – Belgium)
Daniel Thalmann (Virtual Reality Lab – Switzerland)
David Arnold (University of Brighton – UK)
Erik Champion (Massey University – New Zealand)
Eva Zányi (University of Warwick – UK)
Fotis Liarokapis (Coventry University – UK)
Graeme Earle (University of Southampton)
Holly Rushmeier (Yale University – USA)
Kriste Sibul (ICOM-CC – Estonia)
Jean Angelo Beraldin (National Research Council – Canada)
Juan Barcelo (Universitat Autònoma de Barcelona – Spain)
Michael Ashley (University of California at Berkeley)
Milena Dobreva  (Institute of Mathematics and Informatics – Bulgaria)
Karina Rodriguez-Echavarria (University of Brighton – UK)
Luis Paulo Santos (Universidade do Minho – Portugal)
Mercedes Farjas (Universidad Politécnica de Madrid – Spain)
Nadia Thalmann (MIRALAB – Switzerland)
Paolo Cignoni (ISTI – CNR -Italy)
Robert Sablatnig (Vienna University of Technology – Austria)
Roberto Scopigno (ISTI-CNR – Italy)
Sofia Pescarin (CNR – Italy)
Stephen Stead (Paveprime Ltd – UK)
Vittore Casarosa (CNR – Italy)
Maria Theodoridou (FORTH – Institute of Computer Science – Greece)
Bianca Falcidieno (CNR – Italy)
Isabelle Bloch (ENST – France)

Abstract submission (full/project/short/workshops/tutorials/VAST-STARs): 12th May 2009 (23:59 PTZ)
Paper submission for full papers and short papers: 15th May 2009 (23:59 PTZ)
Author notification: 21st June 2009
Camera-ready: 28th June 2009

Conference Web Site: http://www.vast2009.org/
Event Chairs: Kurt Debattista, Sandro Spina – org_committee<at>vast2009.org
Program Chairs: Cinzia Perlingieri, Denis Pitzalis – prog_committee<at>vast2009.org
General Info/Organisation/Logistics: Sandro Spina – info<at>vast2009.org

Google Maps & Cultural Heritage

From Cameron Chapman at Mashable comes a list of the 100+ best tools and mashups; below are the ones I’ve selected that may be of interest to readers of this blog:

Cassini – An overlay of 18th century maps over Google Maps that lets you adjust the transparency of either layer.  (I’ve got copies of the IGM maps of Central Italy from the early 20th century that were used by Ward-Perkins and the rest of the BSR team during the South Etruria survey – I’d love to get those done similar to this application, but I expect I’d run afoul of one or several intellectual property issues…)

BibleMap.org – An interactive map of locations from the Bible.

World Heritage Google Map – A Google Map of UNESCO World Heritage Sites worldwide that includes photos.

PlaceOpedia – A map of Wikipedia articles linked to their locations.

World’s Creepiest Places – Just as the name implies, this map shows information about the world’ creepiest places.

The Kremer Collection – Use a Google Maps interface to browse a large collection of paintings.

zkimmer – An online publication viewer for newspapers and magazines that uses the Google Maps UI.

Google Maps Recent Edits – A constantly updating map that shows the most recent edits to Google Maps.

We Tell Stories – A map of the stories of six different authors that lets you follow the trail of their stories around the world

Map Builder – A quick and easy Google Maps mashup builder.

MapMyPage – A simple tool to put Google Maps on your website.

Map My Life – An easy to use mashup that will map your life and show a timeline using an XML file you provide.

The Google Maps Image Cutter – A free application for cutting any image into tiles for use with the Google Maps interface.

Automatic Tile Cutter – Another app for cutting any image into tiles to use with Google Maps.

GMapCreator – A tool to make creating thematic Google Maps easier.

Geo Twitter – GeoCode your tweets and plot them on an embeddable map.

Mapmsg.com – An app that lets you put a message (smoke signals, crop circles, etc.) into a map and then email it to anyone.

Dual Maps – Free mapping tools to combine different Google Maps views as well as Microsoft Virtual Earth maps.

maps-for-free.com – Get relief layers for Google Maps free for creating your own mashups.

HeatMapAPI – Use this API to create your own heat maps to overlay Google Maps.

PdMarker – An app to help you easily customize Google Maps marker behavior

The original list lives here

Neogeography, Gaming and Second Life

Archaeologists, take note of work coming out of CASA at UCL in the UK:

[two issues are addressed:] firstly that spatial data is still inherently difficult to share and visualise for the non-GIS trained academic or professional and secondly that a geographic data social network has the potential to dramatically open up data sources for both the public and professional geographer. With our applications of GMap Creator, and MapTube to name but two, we detail ways to intelligently visualise and share spatial data. This paper concludes with detailing usage and outreach as well as an insight into how such tools are already providing a significant impact to the outreach of geographic information.”

Now, this is work that has obvious archaeological implications.

On another note, the same group is implementing ABM in Second Life. I particularly like the screen-grab of an escaped agent wandering off into the Metaverse. There’s something profoundly disturbing about that…



The Space Between: The Geography of Social Networks in the Tiber Valley

The following is somewhere in the publication chain, and has been there since about 2004. Reference:

(in press) ‘The Space Between: Places and Connections in the Tiber Valley’ in Coarelli, F. and Patterson, H. (eds) Mercator Placidissimus: the Tiber Valley in Antiquity. New research in the upper and middle river valley. (Proceedings of the Conference held at the British School at Rome, 27-28 Feb. 2004). Rome. British School at Rome – Edizioni QVASAR.

The Space Between:

The Geography of Social Networks in the Tiber Valley

In a Far Side cartoon by Gary Larson, a man with a crumpled map wants to get from point B to point A. The farmer responds, ‘Beats me, sonny. Most people want to go the other way’. The joke underscores the fact that most people have a mental diagram of how places interconnect. That mental diagram is laid out as a list and it depends on the sequence of way-points along the way, a series of connections from place to place. It is more like the London Tube map than the OS or IGM maps.

In the Roman world, space was understood as an itinerary, as a sequence of what comes next[1]. In the Tiber Valley Project[2], we use a GIS to understand the spatial relationships between sites and places, with a very Euclidian understanding of space as a plane viewed from on high. How we represent space, and how the Romans understood space, are completely at odds with one another, and so we miss important elements of the experience of living in the Tiber Valley. When viewed from on high, it is too easy to put too much emphasis on ‘South-Etruria’, ‘Sabina’, ‘left bank’, ‘right bank’ and the ‘Tiber as a Barrier’, as mental categories, almost in isolation from one another. Recent work by Horden and Purcell puts the emphasis on understanding the ancient Mediterranean as a series of interconnected micro-regions[3]. They argue that we must understand the connections to understand ancient life. Yet, we use the GIS simply to represent locations, rather than to understand what might be called a ‘geography of relations’. We neglect that places were understood in the past to have particular relationships with other places, and the way we use GIS reinforces this neglect[4].

What happens if, informed by a network perspective, we look at the geography of the Tiber Valley from a point of view that puts the emphasis on those interconnections? The ‘science of networks’ has developed rapidly over the last few years[5], and it is expressly concerned with understanding the processes that occur on the network structures we find. That is, if we have put dots on the map, the science of networks might be able to tell us something of what happened in the space between those dots and what those dots represent. Batty makes the important point that what might appear to be random in Euclidean space (our dots on the map), can in fact be rather ordered in terms of networks[6]. This paper concentrates first on the problem of representing these connections, and then turns to possible avenues to explore their meaning. It aims to demonstrate the potential power of a network science point of view for understanding the Roman world.

Representing space

In this volume, there are many maps of the middle Tiber Valley. North is always at the top of the map. There is no real reason why we do this, other than the dictates of convention. Since that is how we learn to read maps, that is why we do it. But it does have an effect on how we interpret the information displayed on the map. Rome is always at the bottom of these maps. Even if we did not know a single thing about the City of Rome, there is an implicit assumption, by displaying the map in this way, that everything and everyone must make its way to Rome.

There is empirical evidence to suggest that how we display information on a map affects how we interpret it[7]. At conferences or in the lecture hall, even the size of the screen has an effect on how we interpret the interrelatedness of the information displayed, especially when we are displaying point-data. Researchers have discovered that, when viewing point-data displayed on a screen (what the viewers implicitly recognize as a map), people are more inclined to associate points together in the vertical dimension, rather than in the horizontal.[8] That is, up-down relationships are more likely to be seen in the patterning, rather than left-right. Viewers tend to regard points in the up-down dimension as being more alike, more similar, even when the distance between them is exactly the same as for the horizontal points.

Is the Tiber a barrier or a bridge? When we display the information in our GIS as convention would dictate, we naturally focus on north-south relationships, rather than east-west. We should rethink that. Set your GIS to display maps with west at the top, and see what else becomes apparent. Fig. 1 represents the distribution of stamped bricks (from the British School at Rome collection) in South Etruria. There is seemingly no pattern to this distribution, at least by eye. But when the same information is displayed as in fig. 2, with a 90° rotation, suddenly east-west and trans-Tiber connections jump to the fore (compare with fig. 6 below).

If how we display and represent space affects how we interpret the importance of relationships between places, should we expect the Roman conception of space to have had any different effect? We can approach this problem of understanding the connections between places from another angle, this time using our best guide to the Roman understanding of how places are connected: the Antonine Itineraries. In the Itineraries, the sequence of towns to visit to get from one part of the empire to any other part is listed. Instead of looking at these itineraries plotted on a map, we can follow the lead of Henry Beck, the inventor of the Tube Map, and represent the Itineraries as a network diagram, where the points are the towns, connected to the next town in the itinerary. This network diagram is a social network diagram, because it indicates something of the social, commercial, and cultural interactions between individual towns (for why else would one want to get from town A to town B?).

Geography and social network analysis

Some urban geographers now argue for an understanding of cities and settlement structures in terms of social relationships and their intensity where different social networks intersect[9]. Social life works across various networks, and cities are the foci of multiple overlapping social networks (think of the Third-World immigrants in modern Rome who peddle trinkets to North American tourists. Here in one city are two worlds that overlap, occasionally touch, but are entirely foreign to one another). Networks extend beyond the city, linking different cities together in different ways, but they also incorporate every point in between along the continuum of settlement types from humble rural farmsteads upwards. In this view, cities themselves are nodes of social relations in time and space. At any given time a city will be a node in any number of different networks of power and influence[10].

Networks do not exist independently of the people within them, and it is not enough that mere interconnections should exist. Individuals matter. Individuals must make something of these interconnections, for the networks to work[11]. This idea can be seen to underlie Laurence’s recent discussion of the transformation of Britain into a Roman province[12]. He explicitly considers the Itineraries as evidence for the purposeful reconfiguration of existing networks, over which people, goods, and capital flowed, into a distinctly Roman pattern.

An example from Italy concerns the creation of fora (market-centres) and the process of establishing control in newly centuriated land, instances where individual élite intervene in the landscape. This process represents the conscious decision to warp and reconfigure local network patterns[13]. This process is visible at Forum Novum, a settlement established in the 2nd century BC, upstream from Rome along the Aia tributary of the Tiber, in the Sabina region. A town centre was built, as well as a market for the surrounding farms. There was much ostentatious display and the typical self-aggrandizement of the local elite who paid for the development, including an aqueduct and an amphitheatre for games[14]. Yet, it never grew into a town as such, and there was little in the way of housing. Even today its modern successor, Vescovio, is not much more than a church and a restaurant. After the initial capitalization on the intersecting trade and farming networks in the river valley where Forum Novum is situated brought the settlement into being, those networks were evidently not sufficient to transform it from a minor centre. This is because of its end-point positioning in relationship to other settlements in the networks of trade and communications in the Tiber Valley, more on which below.

A network approach to cities and settlements can be more than metaphorical. Social network analysis[15], which normally considers the ‘vertices’ or ‘nodes’ in a network to be individual persons, can be adapted for our purposes to look for connections within and across cities and space. This is why we reconsidered the Itineraries as a type of social network. Then we can ask, what does position here vis-à-vis other ‘nodes’ imply for the dynamics of interaction and the overall global structure? When we consider the connections between towns today from that perspective, we find occasional long distance links. These are the motorways and so on which allow travel from one city to another without stopping in the little towns in between. These long distance links are important, because they let information travel across the network in a much quicker route than would otherwise be possible. They turn the network into what is known in network science as a ‘small-world’[16]. A small world is simply one in which, locally, most ‘nodes’ (be they people or cities) are tightly linked to neighbouring nodes, but a few long-distance connections have the global effect of shortening the average number of steps it takes to get from one node to any other node chosen at random, as in fig. 3[17]. That is to say, global characteristics of the network emerge from local interactions. When the lights went out in North America, London, and Italy in the summer of 2003, this was because the electricity grid has similar long distance connections that allowed errors to travel quickly and accumulate. In an economic network, the same ‘small-world’ principal allows capital to accumulate and be used effectively. In a social network, it allows certain people to become indispensable because they effectively can control where the information goes. They can control who knows what.

The Itineraries do not have any of these long-distance connections (fig. 4). The Roman world was not ‘small’ in the sense described above. There are some sea-connections in the Itineraries, but not enough to actually affect the way information travels through such a network. This means that, from a network analysis point of view, the interconnections between towns in the Empire are exceedingly fragile. Only a few ‘links’ would have to be broken, for the whole network to appear fragmented. Throughout human history, the majority of people never travelled much further than a handful of miles from their place of birth. Geographic knowledge of distance places therefore had to be provided through some other agency. On this evidence, to the Roman who wanted to travel some distance using these Itineraries, it would not take much bad news to persuade him that a particular route was blocked.

Yet appearances can be deceiving

When we actually examine the road network (fig. 5, a detail of the Roman roads around Rome), it is clear that there are many alternative routes, many different ways to get from point A to point B. This discrepancy is the crux of the matter. The global picture of how places interact available to a Roman in the form of the itineraries provides only for a limited number of ways to get from A to B, while the local picture, known to the people who live in an area, suggest multiple pathways.

Batty argues that in transportation systems, the adding of new layers to existing systems – such as canals to road networks, rail to canal networks – has the effect of creating small-world conditions[18]. In this sense, the cursus publicus as a rapid specialized communications system for the Emperor[19], overlaid on the existing transport system, may have created small-world conditions for the Emperor’s intelligence network, with all the attendant implications for wealth and knowledge condensation[20].

Local routes and pathways

To understand local multiple pathways, and their implications for how geography was understood, the gravity settlement model developed by Rihll and Wilson[21] was used to study the interconnections between sites using stamped brick, identified during the South Etruria Survey, in the Tiber Valley. Rihll and Wilson’s process works on modelling the amount of interaction between places, based on the assumption that places closer together will be more likely to interact, than places further apart. This mathematical model is not built on any other geographic information, other than the relative positioning of each site, based on its x and y coordinates. While a multitude of sites used brick, comparatively few used stamped bricks. Not every brick was stamped, of course, but the presence of a stamped brick probably indicates a larger shipment of brick. Patterns of supply can reflect the social ties of the builders, so the distribution of different stamp types can be used as an indicator of the degree to which the owners/builders of a site were engaged in the games of competitive display with each other, both in the countryside and the Metropolis[22].

What was interesting about this model applied to the Tiber Valley was the way it suggested interactions changed over time (fig. 6, the output from this model). To the naked eye, the distribution of sites using stamped brick does not appear appreciably different from one period to the next. Yet, to the model, subtle differences in positioning create different network patterns of interaction. At some periods, strong trans-Tiber connections are suggested amongst sites using stamped brick; other times, more north-and-south connections; sometimes certain main roads are implied, such as the via Cassia; other times, the use of the Tiber is implied as the route for these interactions. It is interesting to note how the east-west connections suggested by this model recall the same connections apparent to the eye when we turned the map in fig. 1 ninety degrees. These are as much social interactions as geographical interactions, and so suggest a much more complicated geography than one in which every product uniformly makes its way to the bottom of our map, to Rome.

These interactions also are implied in the archaeometry of stamped bricks. Seventy-five stamped bricks from the Tiber valley were tested using X-ray fluorescence[23]. The results were then correlated with the information on the stamps. Contrary to what we would expect it seems that not all bricks carrying the same stamp type were made from the same clays. There are also cases where multiple land-owners exploited the same clay sources. Some of the tested bricks were transported up the valley from where they were made; others were transported down stream; still others from one side of the valley to the other. This seemingly goes against our functionalist, cost-of-transport view of the economy, but it does point to a somewhat neglected side of the consumer city model: the social relationships that mediated trade[24].

The local and the global

Assume for a moment that all trade flows downstream, and like the Roman informed by the Antonine Itinerary we recognize only one route from point A to point B. It is here, in the discrepancy between local and global knowledge of geography, that an individual or community can make money and impact the economy. In trade, it is not the cost that matters so much as the profit that can be made. So for the well-connected individual (as in fig. 7) it should be easy to work out the discrepancy between the local and the global – between what she knows, and what her buyers know. It is ‘she’ because the single most important individual in the social network of the brick industry, the individual who sat in the very centre, was Domitia Lucilla, mother of Marcus Aurelius[25]. Over 200 people can be connected to her in only a few steps, making the industry a small-world, and putting her in a position to control the flow of information in the trade. She would have known, as a function of her position in the network, about clay sources and building contracts, about the amount of profit that could be made for a given distance of trade, whether upstream, downstream, overland, or overseas. To be able to call on clients, to be able to use the resources of skilled slaves, to have the right connections, allowed Domitia Lucilla and other well-connected individuals to get the material to where it was wanted with a minimum of fuss.

However, because of the way geographic knowledge was formulated in the Roman world, the perception of cost-of-transport could well have been out of kilter with the reality. The person buying would not necessarily have known the routes, the difficulties, except in the broadest possible terms. That meant that the buyer would find a certain cost level to be acceptable, even when that cost was in reality much higher than circumstances should have actually dictated. Today it would be similar to the way that, if we are not plumbers, we are at the mercy of the “cow-boy” who tells us the work is going to take longer and cost more than in truth it does. Most emperors were not, almost by definition, stupid men. Why do they invest so much in the brick trade? It may be that a significant factor is the discrepancy between the local and the global which makes the otherwise humble building trade economically valuable (remembering that brick making was an adjunct to agriculture), and allows it to function in the way that is visible archaeometrically. This is in line with what people such as Janet DeLaine have suggested concerning ideologies of construction, and the use of so-called ‘exotic’ materials[26]. ‘Exotic’ was in the eye of the beholder, and could even apply to something as humble as brick, if it seemed that it was difficult to obtain. That difficulty depended on how one perceived space, and the interconnections between places.


In the Tiber Valley, the relationships between places change over time, and they are not in the patterns we expect. As Batty argued[27], we need to move from representing locations, to representing relationships. If merely we study the ‘dots on the map’, we miss important facets of the way the social and economic geography of the Roman world worked. ‘Dots on the map’ represents a local understanding of space. To get to the global, as preserved for us in works such as the Antonine Itineraries, we need to explore the space between the two levels. Network science offers us a formal methodology for exploring the space between the local and the global. Networks are not static, nor are they deterministic. They evolve, for they change in response to the decisions people make, but they also influence those decisions. They can even make brick exotic.


In displaying archaeological information as points on a map, we lose elements of the social and economic geography of the region we are studying. This paper suggests a methodology for exploring the space between our ‘dots-on-the-map’, based on the rapidly developing ‘science of networks’. It takes as a case study the distribution of sites using stamped brick in the Tiber Valley. It suggests that contradictions between local and global understandings of spatial relationships were exploitable economic opportunities.

Visualizzando i dati archeologici come punti su una mappa, perdiamo elementi della geografia socio-economica dell’area che stiamo studiando. Questo contributo suggerisce una metodologia per esplorare lo spazio compreso tra i “puntini”, basata sui costanti sviluppi della “scienza delle relazioni”. Come esempio, si è scelto la distribuzione dei bolli laterizi nella valle del Tevere. Tale esempio suggerisce che le contraddizioni tra le percezioni locali e globali delle relazioni spaziali potevano essere sfruttate a livello economico.


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Acknowledgements: Thanks to Mark Wakefield for the computer modeling. Thanks also to Thea Politis, and Rick Valin for comments, and to the BSR for access to the South Etruria Collection of stamped bricks. Errors remain my own. The original research was supported by the Social Sciences and Humanities Research Council of Canada and the Overseas Research Studentship Scheme administered by the Committee of Vice-Chancellors and Principals of the Universities of the UK.

[1] Brodersen 2001.

[2] Patterson-Millett 1998; Patterson 2004.

[3] Horden-Purcell 2000.

[4] Cf. Batty 2003, pp. 2-3 on the difference between ‘Geographic Information Systems’ and ‘Geographic Information Science’.

[5] Barabasi 2002; Watts 2003 for recent syntheses of the topic.

[6] Batty 2003, p. 5.

[7] Montello et al. 2003, pp. 316-331.

[8] Montello et al. 2003, p. 317.

[9] Massey et al. 1999, p. vii.

[10] Massey et al. 1999, pp. 42-49, 100-136.

[11] Massey et al. 1999, pp. 161-163.

[12] Laurence 2001a.

[13] Cf. Laurence 2001b, p. 596, 598 on the space-economy of Roman Italy.

[14] Gaffney et al. 2001.

[15] For the basics of which, see Wasserman-Faust 1994.

[16] The most accessible discussion of the characteristics of a ‘small-world’ is Watts 2003, pp. 69-100. Cf. also Watts-Strogatz 1998.

[17] Watts 1999.

[18] Batty 2003, pp. 18-20.

[19] Cf. Kolb 2001.

[20] Bouchaud-Mézard 2000, p. 536, and Buchanan 2002, pp. 195-196.

[21] Rihll-Wilson 1991.

[22] Graham 2002, pp. 100-7; Graham forthcoming on using the Tiber as infrastructure; cf. De Laine 2002.

[23] Graham 2002, pp. 52-73.

[24] Wallace Hadrill 1991

[25] Cf. Graham forthcoming on controlling the brick industry.

[26] De Laine 2002

[27] Batty 2003