I would like to model the dimensions of the trade areas for a group 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. 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?