The final project assignment for GIS Applications for Archaeology dealt with cost analysis. The ultimate outcome for both parts of the project was a least cost path, which is essentially a route from point A to point B that GIS has calculated as being easier to travel than any other possible route, based on the data provided and the parameters set by the user. In this case, we used slope (i.e., it's generally easier to cross flat terrain than to climb up a steep hill) and land cover (i.e., forest vs. agricultural fields vs. the ocean) to determine how hard each pixel would be to cross in the real world--the "cost" of traveling that way. Slope and land cover data are classified according to difficulty of passage and then used to create a weighted overlay raster which then serves as the basis for the cost distance and cost path calculations, which ultimately result in ArcGIS's idea of the optimal route between two points. (For a route with multiple points, you have to run each leg as a separate analysis.) Because this is a somewhat complex, multi-step process, we used Model Builder to set up the analysis rather than running the tools one at a time.
For the first part of the project, in which we learned how to perform the analysis, we examined routes between three prehistoric archaeological sites in Panama:
For the second part, we had a choice of subjects but were on our own to acquire the necessary data and set up the model. I chose to try to reconstruct the route of the Camino de Mulas, a historic mule trail in Costa Rice and Panama. I had to run the model one or two steps at a time rather than all at once because the processing times were extremely long, probably because of the size of the raster files I needed to cover the whole study area. In the end, it looks like some of the trail may have been where the Pan-American Highway is now, but other sections of it may have escaped destruction. That's making a number of assumptions about how "right" the least cost path is, though. It would take a lot more research to figure out if this route actually makes sense (especially since the analysis was performed with modern land cover data that ignored rivers), let alone to determine whether it's the right one. Still, it's a starting point and an interesting way of looking at history.
