Alessio Palmisano, Stuart Brookes and Andrew Reynolds
UCL Institute of Archaeology
It is axiomatic that travel and transportation in the human past adapted itself to physical obstacles in the landscape. Amongst these, terrain, water features, vegetation, and surface conditions, were powerful influences on the transportation geography. So too, might they be modified by transportation: road improvements, bridges, causeways, or tunnels, were all means by which natural obstacles could be overcome, but these required corresponding levels of cooperative action, labour, infrastructure, and planning. There are intimate relationships too between topography and modes of transport, which range from pack animals to wheeled vehicles and between terrain and the kind of commodities and goods being transported.
In order to examine the effects of the physical landscape on past transportation geography, we have created an omnidirectional landscape connectivity map of England and Wales. Based on a Digital Elevation Model (DEM) of the region, the map attempts to describe the principal paths and corridors as defined purely from the slope of the terrain. This approach allows archaeologists to approximate the complex matrix of accessibility and isolation in a given landscape and to assess to which degree topography could have shaped interaction dynamics of past human communities (see Palmisano 2015). In future work, as part of the project Travel and Communication in Anglo-Saxon England we will examine the further effect on movement of other obstacles such as rivers and vegetation, but it is hoped in the meantime that this map inspires other research on spatial interactions in the past.
The map was created in several steps. First, a friction surface was created from a slope map derived from the Digital Elevation Model (DEM) available from NASA's Shuttle Radar Topography Mission (SRTM) of 2000 (http://www2.jpl.nasa.gov/srtm/). Each grid cell was assigned a resistance value based on the slope degree (see Ericson and Goldstein 1980). Second, we created two pairs of horizontal and vertical parallel strips having zero resistance and used the open source software Circuitscape (http://www.circuitscape.org/) in pairwise option to simulate the flow of current in both west-east and north-south directions (McRae and Shah 2009). Finally, the two resulting current density maps were combined by multiplication in order to generate an omnidirectional connectivity map (see Pellettier et al. 2014).
The resulting map shows a number of sharp corridors of connection (light grey filaments) of different scales and distributions. Other areas (dark filaments) were less well connected. This omnidirectional connectivity map can be used quantitatively to address a range of questions regarding past societies in England and Wales, for e.g.:
- Can particular settlement types be related to 'natural' corridors of movement (e.g. at pinchpoints or 'crossroads', as 'strings' along corridors, etc?
- Is trade, the movement of resources, or cultural contact influenced by 'natural' corridors? Does the distribution of portable objects relate to the distributary network of terrain?
- Does the physical road network complement or cut 'against the grain' of natural corridors?
- How do social, political and territorial configurations relate to natural corridors?
Figure: Omnidirectional map of south-central England and Anglo-Saxon royal vills
Ericson, J., and GoLdstein, R., 1980. Work Space: a New Approach to the Analysis of Energy Expenditure within Site Catchments. In: F. FindLow and J. Ericson (eds.), Catchment Analysis: Essays on Prehistoric Resource Space. Los Angeles: University of California, 21-30.
McRae, B.H. and Shah, V.B., 2011. Circuitscape User Guide. ONLINE. The University of California, Santa Barbara. Available at: http://www.circuitscape.org.
Palmisano, A., 2015. Spatial Approaches to the Political and Commercial Landscape of the Old Assyrian Colony Period. University College London, Unpublished PhD dissertation.
Pelletier, D., Clark, M., Anderson, M. G., Rayfield, B. and Wulder, M. A. and Cardille J. A., 2014. Applying Circuit Theory for Corridor Expansion and Management at Regional Scales: Tiling, Pinch Points, and Omnidirectional Connectivity. PLoS ONE 9(1), e84135. doi:10.1371/journal.pone.0084135