visualization - How can I produce heatmaps based off of player reported data?

For a really good example of what I'm talking about, see how the developer of Replica Island does it based off of Player deaths: http://www.youtube.com/watch?v=7-62tRHLcHk&feature=player_embedded#t=37m

How can I easily produce heatmaps based off of data that I pass in?

Halo 3 is another good example of heatmap usage in game data reporting: http://www.bungie.net/Online/Heatmaps.aspx