Jeffrey Barke has written up a tutorial detailing how to create a density map with Prototype, the Google Maps API and the HeatMapAPI. The heat map API looks cool indeed, and that piece of code looks simple: PLAIN TEXT JAVASCRIPT:   addHeatMap: function() { var heatMap = new GEOHeatmap(); heatMap.Init(this.width, this.height); heatMap.SetData(this.data); var preUrl = heatMap.GetURL(); var heatmapOverlay = new HMGoogleOverlay(preUrl); this.map.addOverlay(heatmapOverlay); }