Implements the friction surface used to create cost-buffers around sets of spatial points based on the caloric cost of travel. See Hill et al. 2015 in Advances in Archaeological Practice for more.
Hill, J. Brett, Matthew A. Peeples, Deborah H. Huntley, H. Jane Carmack. (2015). Spatializing Social Network Analysis in the Precontact U.S. Southwest. Advances in Archaeological Practice 3(1):63-77.