Evaluating inputs to models of hominin raw material selection: map resolution and path choices

Abstract

Selection of an appropriate scale is an important decision in study design in many branches of science, since perceived patterns often change with the scales of spatial extent or resolution of an analysis. In previously published work, we created a resource selection model to determine the importance of several independent variables for the selection of lithic materials by hominins at a Middle Palaeolithic site in southern France. Two of these independent variables (calories exerted and difficulty of the terrain covered in travel from source to site) were calculated using elevation data extracted from maps. In the present paper, we examine the differences in model performance when the variables ‘Calories’ and ‘Difficulty’ are calculated using 1) three base maps for elevation that differed in map resolution (from finest to coarsest: a 1:25,000 topographic base map, SPOT DEM, and SRTM DEM), and 2) two different methods for determining the route from source to site (straight-line route and least-cost route; both methods exclude areas with slopes >60% from travel). Our best model was the one that used data calculated using the topographic base map; however, the SRTM DEM-based data produced models of essentially equal quality. Regardless of map scale, models that used data calculated using a straight-line route always outperformed models that used data calculated using a least-cost route. This supports our previous finding that a straight-line route is a more appropriate measure for the path from lithic source to site than a least-cost route. We conclude that the map resolution of each of the base maps used here is appropriate for analyses involving spatial data pertaining to Neandertal activity because this type of data is essentially always coarse-grained.