It looks to me like they are using Google Maps with a FusionTablesLayer (shown as a heatmap).
The maps are not prebuilt. A server (from Google) computes them in real time and send the images to the client (browser) that draws them on the top of the map. I hope it helps! -- You received this message because you are subscribed to the Google Groups "Google Maps JavaScript API v3" group. To view this discussion on the web visit https://groups.google.com/d/msg/google-maps-js-api-v3/-/MaSqKN6ZJrQJ. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/google-maps-js-api-v3?hl=en.
