I’ve mentioned a number of libraries for working with maps, such as the CCHMapClusterController for high-speed map clustering mentioned earlier this year.
Here’s an open source library that allows you to very quickly generate heat maps called LFHeatMap from George Polak.
LFHeatMap generates a UIImage containing the heat map based on a point/value array. The generated image can be overlayed on any view, and there is included functionality for generating heat maps specifically for map views based on CLLocationObjects corresponding to the map coordinates.
Here’s an image from the readme that shows the included demo plotting the magnitudes of the 2011 Virginia Earthquake.
You can find LFHeatMap on Github here.
A nice library for quickly generating heat maps.