I created a tutorial that will step one through how to create a density map with Prototype, the Google Maps API and the HeatMapAPI. The final product, a density map of liquor licenses in Milwaukee, WI, is below. While this map is based on real data, one limitation of the free HeatMapAPI is that only 100 data points can be submitted per call. Since there are approximately 1,300 liquor licenses in Milwaukee, this map isn't even close to accurate!
Creating a map like this takes four simple steps: