The help pages seem to indicate that one needs to start with a point shapefile in order to run GPI in geostatistical analysis. However, it seems to run perfectly well from a polygon shape file. Does this mean that GPI computes and uses the polygon centroids by default? The polygon file I am using is a Census Tiger file which has fileds for x and y interior points. Is ArcGIS by any chance aware of these fields and using them?
I was first using feature to point to get point files from my polygon files. Then, one time by distraction, I used a polygon file directly. Lo and behold it worked. So now I am curious about how it is doing this, as far as I can see, undocumented operation.