A heat map is one of the great innovations of visual communication. In an instant, you can spot a weather formation and judge the seriousness of the storm, or see the heaviest concentrations of U.S. Internet outages.
We're already inundated with too much information — Twitter feeds, status updates, email archives, etc. — but a heat map represents a good way for upper level management to see problems and successes instantly. The heat maps featured here communicate massive data sets in a way that few images can accomplish.