Cumulative viewshed analysis: a GIS-based method for investigating intervisibility, and its archaeological application

This chapter introduces a general method, which may be called cumulative viewshed analysis, which can be used to make inferences about the relationships of intervisibility between related sites within a landscape. Although cumulative viewshed analysis may well find wider application, the method has been developed in response to a particular research problem, namely an attempt to understand the spatial relationship between archaeological monuments. The calculation of a line of sight map or ‘viewshed’ for a point location, given a digital elevation model (DEM) is a relatively trivial computing problem and is available within the current functionality of many GIS. In a raster system the calculation requires that, for each cell in the raster, a straight line be interpolated between the source point and each other cell within the DEM. In situations where the intervisibility within a group of sites is of interest, it is possible to obtain a viewshed map for each site location.