Issues in Replication and Stability of Least-cost Path Calculations

An important and frequently used tool in archaeological spatial analysis is least-cost path (LCP) analysis to compute routes connecting a set of targets. The outcome depends on the cost model chosen and the topographic data used. A slope-dependent cost model requires a digital elevation model (DEM) that should reflect the landscape in the past. It is often impossible to reconstruct the past terrain, and modern high-resolution elevation data results in problematic storage requirements and computation times. This article presents a case study that explores issues in replication and stability of LCP calculations for pairs of targets that are close to known old trade routes. A large number of cost models is tested based on two topographic data sets, including DEMs of two different resolutions (25 m and 50 m). The cost models use six different slope-dependent cost functions suggested by various authors for pedestrian movement. Moreover, a slope-dependent cost function is applied that results in LCPs including hairpin curves if the slope exceeds a predefined critical value. It is shown that the best-performing LCP sets for the two topographic data sets are closely related but not identical. Moreover, reasons for the failure of LCP reconstructions for some old route sections are discussed.