Our final project for GIS 5990 was a substantial research project. I chose to continue with the Valley of Oaxaca data that we had used in the Digitization module. An important anthropological question is whether there is a relationship between population intensity, limitations on the carrying capacity of the land, and a resultant emergence of government. One way to study this relationship is with “site catchment analysis” (Vita-Finzi and Higgs 1970:5) which can be used to determine whether the carrying capacity (the ability of the land to produce food) is exceeded in later cultural phases as populations expand.
The project involved determining the site catchment buffer for the archaeological sites in several 4km square grids within the valley. In the image above, I've created 1 km buffers around the Phase IIIA site for my grids. The sites have been converted to points, allowing me to create Thiessen polygons around each point. Thiessen polygons allow us to divide up an area so that each point on the map is within a region closest to one of the site points. This helps prevent double counting of territory.
With the catchment buffer established, and with the help of land cover shapefiles we had built earlier, I was able to determine how many hectares of each type of land/soil were within the catchment area for each site. This could then be used, along with some information from the literature about corn cob lengths during the various phases and resultant crop yields, to determine the number of metric tons of corn grown around each site. Assuming that a family of five could live on a metric ton of maize for a year, we can estimate the highest possible population supported by the catchment buffer.
In the end, my results showed that the catchment return was quite high and that agricultural limitations do not appear to factor into either settlement patterns nor provide support for the emergence of government in later cultural phases within the Valley of Oaxaca.
