A heat map is a grid of numbers colored by value. I wrote a quick tutorial on how to make the now common statistical visualization. But at some point in the past few years, a heat map came to mean a geographic map with stuff on it. Cartographer Kenneth Field explains what these maps with stuff on it actually are and provides you with the “more established, more accurate and perfectly good terms.”
Extra point for incorporating The Simpsons:
Heat maps have become a popularist way to label a surface representation of data that occurs at discrete points. On one hand the search for a better way of showing point based data which avoids death by push-pin is a sound cartographic approach. Imagine simply looking at a map of points and trying to make sense of the patterns. Chief Clarence ‘Clancy’ Wiggum would certainly struggle to make sense of the pattern of crime in Springfield just from coloured dots.