This readme file describes the landscape data that were used for the least-cost path analyses. ##general notes # All least-cost path analyses were carried out in R version 2.15.2. # All spatial grids were based on the gGraph object 'worldgraph.40k' in the R package geoGraph v.1.0-0 (downloaded from https://r-forge.r-project.org/projects/geograph/) # For details on how to use geoGraph see Jombart T., Balloux F. and Manica A. (2010): 'geoGraph: implementing geographic graphs for large-scale spatial modelling'. # file 'fstlin.txt'contains the linearised genetic distances between all pairs of populations (matrix [G]; see Materials and Methods section for calculation of pairwise genetic distances) # file 'Asin.txt' contains the coordinates of the 17 sampling locations # file 'locations.csv' contains the coordinates of all locations used to reconstruct the Silk Roads network (see Materials and Methods for more details) I) Great-circle distance # Great-circle distances betweeen all pairs of populations were calculated using the package 'fields' in R II) Altitude # The altitude cost grid can be found in the RData object 'topograph.RData' (gGraph object 'topograph') and the script to carry out the least-cost path analyses for the 'altitude' models can be found in the file 'LCP.altitude.r' III) Silk Roads # The Silk Roads cost grid can be found in the RData object 'tradegraph.RData' (gGraph object 'tradegraph')and the script to carry out the least-cost path analyses for the'Silk Roads' models can be found in the file 'LCP.SilkRoads.r' # For the [Water] model (shortest distances on land), all edges that involve nodes representing water (node attributes 'sea' and 'deselected land') were removed, whereas a uniform cost of 1 was assigned to all nodes representing land (node attributes 'land', 'mountain','landbridge','oceanic crossing' and 'coast', as well as all trade routes; for more detail see Materials and Methods)