Global Polynomial Interpolation (GPI) directly from polygon data

[tmuench]

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.

[stevelynch]

The fact that it works with polygons is there for backward compatibility. However, we recommend that you rather use points. You can do FeatureToPoint using the INSIDE option.

Steve

[tmuench]

I presume, then, that the GPI is computing the polygons' centroids and using them for calculating the polynomial. Is that correct?

[stevelynch]

Yes you are correct.

Using the polygons as input would be the same as if you found the centriods using FeatureToPoint with the INSIDE option unchecked and then using that as input to GPI.


The problem with this approach is that often times the centriod falls outside the polygon, a letter C for example.

Steve