I have a fishnet that defines my zones for my analysis, and am interested in the area of different hydrologic soil groups (A, B, C, D) within these zones. Each soil group has a corresponding score (1, 0.65, 0.3, 0.05). I want to calculate a weighted average of the soil group scores for each zone. How do I go about doing this?
The easiest way to do this would be to start by creating two fields in your initial fishnet dataset.
Call the fields
Fisharea in the fishnet. Calculate the area of the fishnet in this field. This is the initial area. Next create a field called
FishID and give each fishnet polygon a unique ID.
Next run the intersect tool between the fishnet and soils layer. Create a field called
FSoilArea. Calculate the area of the polygons in your intersected layer.
Create a new field called
Weight. Take the newly calculated
FSoilArea and divide it by the
Fisharea field. This is the proportion of the soil layer in the fishnet.
Next create a new field called
WSoilIndex. Multiply the
Weight field into the field containing the soil index values.
Take the intersected layer and run the dissolve tool. Select
Soil Type as the dissolve fields. Under the Statistics options select the
WSoilIndex as the input and Sum as operation.
You will now have a Fishnet with the soil indices weighted by area.