Estimating catchment area with contour line

Discussion created by mguaglia on Aug 7, 2012
Latest reply on Sep 9, 2014 by mguaglia
I want to estimate the "catchment" area or service area footprint for a series of hospitals (about 125 U.S. hospitals). I have the geocoded residential addresses of patients for each hospital for a period of time, say 1 year.

I don't think bounding containers such as convex or concave hulls are appropriate because every hospital has a small percentage of patients whose addresses are very far away. For example, a Nebraska tourist may be hospitalized in Boston while on vacation. The Boston container would reach to Nebraska. Not very useful.

My thought is to create density rasters from patient locations. One raster for each hospital. Then for each raster estimate the contour lines that would capture 95% of the volume of patient density. I might have to adjust the cut-point higher or lower than 95%, but as long as it is consistent across hospitals that would be okay.

Unfortunately I don't see an easy way to do this for 125 hospitals. For a single hospital I might be able to determine the 5th percentile cut point of raster intensity and use that in the "contour list" tool. But:

1. I am not sure that is the same as estimating 95% of patient density, and
2. It is not practical to do this manually for 125 rasters.

I realize that Geospatial Modeling Environment might have what I need, but it is difficult in our IT environment to get that installed on our server. (Not impossible, but it is an option.)