I did some work on Voronoi a few years ago. I made an overlay in Voronoi transparent colored cells that would show for example where the nearest convenience store was to a given location in the city and this would overlay the regular map of the city. I was going to try to sell these to the convenience store as they always had a map of the city they were in somewhere in each store. An improvement would be to run a google map from each store to each house and actually use the mileage to the store the store. This would account for rivers etc that would block the shortest path. There is probably an idea for a startup somewhere there....