"Zonal statistics" for two polygon layers using ArcMap

Question

I have 2 polygon layers:

• one is a vector grid with attribute values for each "polygon cell"
• the other including administrative boundaries

I would like to calculate the mean value of all attribute values within each polygon of the administrative boundaries.

I know that ArcGIS offers the Zonal Statistics tool, but I would have to convert everything to raster. I know of the GME extension which includes a polygon in polygon analysis. But I was wondering if there is any built-in function within ArcMap?

Answer 1

There is no built in function for a precise result as far as I know, but you can achieve that in a few steps (and later automate it in python script or model builder)

1. "Union" the two feature classes

2. "add field" to the result of the intersection

3. "calculate field" with the value of your grid vector multiplied with the area of each new polygon

4. "summarize table" with the sum of the area and the sum of the new field , based on the administrative code

5. "add field" on the resulting table

6. "calculate field" to divide the sum of the value*area by the sum of the areas

That's it, you have the weighted mean value for each administrative code. You can join this table to the polygon feature class if needed.

Rem: with shapefiles, you will need to compute the area of the unioned polygons (this is done automatically in geodatabase)

Answer 2

You can use spatial join if you can afford some approximation (that is, if the cells are much much smaller than the administrative polygons.

Then you just need select Join on_to_one option, and define the field mapping as "mean". The difference with my previous answer is that a cell that overlaps two administrative polygon has the same weight than a cell that is fully included. You can change the matching option (e.g. intersect or completely_within) to fit to your needs at best, but the area of the polygon will not be divided.

As a remark, the result with zonal statistics of a raster with rasters would correspond with HAVE_THEIR_CENTER_IN match option (with a raster resolution and origins identical to the characteristics of your vector grid)