I have no idea how Yelp has implemented this but I've done Heatmaps before. Basic process I built relied on caching map tiles. Pre-compute your raw data by la

I have no idea how Yelp has implemented this but I've done Heatmaps before. Basic process I built relied on caching map tiles. Pre-compute your raw data by lat/long. Build that into map tiles you overlay on the map by determining map area and converting lat/long to pixels on the tile. Load new tiles as the map is panned. Do it quickly if you want users to be happy. Cache everything.