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


From   "Dimitriy V. Masterov" <dvmaster@gmail.com>
To   Statalist <statalist@hsphsun2.harvard.edu>
Subject   st: how to model the size/shape of an area
Date   Tue, 8 Nov 2011 10:27:19 -0500

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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