st: how to model the size/shape of an area

["Dimitriy V. Masterov" <dvmaster@gmail.com>]

I would like to model the dimensions of the trade areas for a set of
stores. I have geocoded sales data for each store, which I used to
construct a convex hull using a GIS program. Essentially, I took the
nearest 80 percent of sales for each store, and then snapped a rubber
band around those points to get a trade area boundary for each store.
Then I calculated the area of these regions, and modeled the radii as
if the trade areas were circles, using the characteristics of the area
right around the store as predictors. I used a simple glm model with a
log link function for the estimation.

This gives terrible predictions since many of the areas are elliptical
or have spike-like bulges. Does any one have any suggestions for how
to model the shape and size of these regions in a better way?

DVM
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