Shapefile with overlapping polygons: calculate average values
I have a very big polygon shapefile with hundreds of features, often overlapping each other. Each of these features has a value stored in the attribute table. I simply need to calculate the average values in the areas where they overlap. I can imagine that this task requires several intricate steps: I was wondering if there is a straightforward methodology. I’m open to every kind of suggestion, I can use ArcMap, QGis, arcpy scripts, PostGis, GDAL… I just need ideas. Thanks!
Answer
You should use the Union tool from ArcGIS. It will create new polygons where the polygons overlap. In order to keep the attributes from both polygons, add your polygon shapefile twice as input and use ALL as join_attributes parameter.This creates also polygons intersecting with themselves, you can select and delete them easily as they have the same FIDs. Then just add a new field to the attribute table and calculate it based on the two original value fields from the input polygons. This can be done in a script or directly with the toolbox's tools.