Special Overlay: An ArcPy Tool

In May of 2014, I partnered with fellow masters student Agata Miszczyk to develop a custom tool for ArcGIS using ArcPy. We submitted this work as a final project for our GIS Programming course.

The Special Overlay tool allows you to aggregate data from one polygon layer to another, even when the boundaries do not match. This is done by determining the percentage of a given polygon from the input features that falls within a given polygon in the overlay features (study area), then assigning that percentage of the value from the input polygon to the overlay polygon. In the field of Geographic Information Science, this process is known as areal interpolation (Goodchild & Lam, 1980).

This approach to areal interpolation assumes that the data is evenly distributed throughout each polygon. This, of course, is rarely the case, but it is a common assumption to make when no better alternative is possible.

Read the full text of our project report here or in the embedded PDF below. You can also check out the python script on github:

Work Cited:

  • Goodchild, M.F., and Lam, N. S-N. (1980) Areal interpolation: a variant of the traditional spatial problem. Geo Processing, 1, 297-312.