Heat maps are a visual representation of data wherein each value in a matrix is represented with a color. It has been widely observed among the visualization community that color as a visual cue is ranked toward the bottom when compared with other tools such as position, length, angle, and so on. The traditional heat map is represented in a rectangular format, but at the very basic level a heat map is representing colors for numbers. An interesting implementation of heat maps is its integration with a calendar. We will study the calendar heat maps in detail in the recipe Generating interactive calendar maps in Chapter 7, Data in Higher Dimensions.

The Iraq body count is a database that maintains records of violent civilian deaths since 2003. The heat map clearly shows that the most civilian deaths occurred in the 2006-2008 period and it declined thereafter. Heat maps have a much better application to data such as stock prices, sports data, and biology (to study the levels...