Madness part 1: visibility networks

ALL_SEEING_EYEI recently wrote I would keep you posted on my two months of madness in the run up to completing my PhD. Turns out I have very little time to write blog posts now … who would have guessed?!? But just to get things started, here is the first one. Let’s talk about the networks we can create using our eyes, let’s talk about visibility networks! I want to encourage everyone to comment and discuss these posts, I would really benefit from your input as I wrap up this four-year long struggle with the PhD beast.

One of my PhD’s case studies is on visibility networks. What are those, you ask? Well, they don’t really exist. That is to say, they are useful abstractions of possible past social phenomena. I use networks to represent whether past individuals standing on one point in a landscape, like a settlement, could see some other point in the landscape I am interested in, such as another settlement. This figure shows you how such a network could be created: an individual with a certain height standing on site A can see site B which is positioned somewhere else in a landscape, only if the view is not obstructed by hills or mountains. You can then represent this individual and the point he/she observes as points (or nodes in network terminology) and the line of sight from the observer to the observed point as a directed line (or arc in network terminology). Do this for tens or hundreds of observation locations and a complex network of lines of sight emerges.

JAMT_Brughmans-etal_fig5NEW

Many people have asked me why this is useful. What do visibility networks add to existing approaches to studying past landscapes and settlement patterns, such as viewsheds in GIS for example? I like to believe I have a pretty good answer to this. Sometimes archaeologists are interested in understanding a past phenomenon that concerns the potential interactions between two entities, in which cases networks offer the best representation and analysis technique. To give an example, if we are interested in studying a past communication network that used fire or smoke signals to share information from one settlement to another (Like in Disney’s Mulan or in The Lord of the Rings), then evaluating the visibility of an entire landscape is overkill. All you need are the points and the lines. We do not have to analyse whether every square meter of a landscape was visible, but just that one point of interest. So selecting the best conceptualisation and abstraction of the past phenomenon you are interested in understanding can save you quite a lot of computing time. And it allows you to focus on representing and exploring your hypothesis, and not get distracted by other questions (if focus is what you want of course).

Mulan by Walt Disney
Mulan by Walt Disney

Moreover, we can do so much more once we have abstracted and represented our information about such a past communication system as a network. We can use network analysis techniques to determine the structure of this network, to compare it to other communication networks, to evaluate how efficient it was at sharing information, which settlements were key in sharing or blocking information, and so on. All of this offers a fresh new look on our data and provides results that can feed into our archaeological discussions and imaginations. Of course, the numbers a network analysis spits out are never the final word. They should always be re-contextualised in a wider archaeological research context rather than being taken at face value, or as an extra piece of  “primary information”.

I am definitely not the first archaeologist to have come up with the idea of visibility networks. Although it is not a very common topic, it has been done every once in a while in the past four decades, as you can see from the bibliogrpahy below this post. Many archaeologists focused their efforts on understanding signalling networks as described above (e.g. Shemming and Briggs, Swanson, Ruestes Bitrià). Another common phenomenon is the study of visual control, a popular topic in the study of Iron Age Spain (e.g. Grau Mira). There we see large fortified settlements on hilltops often called oppida, surrounded by smaller rural settlements. The oppida are often inter-visible with the rural settlements, whilst the rural settlements are less commonly inter-visible with one another. Archaeologists have suggested that this allowed for the oppida to visually control the smaller settlements, that it tells us something about social interactions between these communities, and possibly even about settlement hierarchies.

In following blog posts I will be giving you some more information about my efforts to explore such hypotheses of visual communication and control in Iron Age and Roman Southern Spain. Stay tuned!

Any thoughts or comments? Don’t hesitate to get in touch!

Archaeological studies of visibility networks:

Grau Mira, I. (2005). Romanization in Eastern Spain: a GIS approach to Late Iberian Iron Age landscape. In J.-F. Berger, F. Bertoncello, F. Braemer, D. Gourguen, & M. Gazenbeek (Eds.), Temps et espaces de l’homme en société, analyses et modèles spatiaux en archéologie. XXVième rencontres internatioales d’archéologie et d’histoire d’Antibes (pp. 325–334). Antibes: Éditions APDCA.

Grau Mira, I. (2004). La construcción del paisaje ibérico: aproximación SIG al territorio protohistórico de la Marina Alta. SAGVNTVN (P.L.A.V.), 36, 61–75.

Grau Mira, I. (2003). Settlement Dynamics and Social Organization in Eastern Iberia during the Iron Age (Eighth-Second Centuries BC). Oxford Journal of Archaeology, 22(3), 261–279. doi:10.1111/1468-0092.00187

Ruestes Bitrià, C. (2008). A Multi-technique GIS Visibility Analysis for Studying Visual Control of an Iron Age Landscape. Internet Archaeology, 23, http://intarch.ac.uk/journal/issue23/4/index.html.

Shemming, J., & Briggs, K. (2013). Anglo-saxon communication networks. http://keithbriggs.info/AS_networks.html [accessed 4-10-2013]

Swanson, S. (2003). Documenting prehistoric communication networks: A case study in the Paquimé polity. American antiquity, 68(4), 753–767.

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