Heat map

A heat map is an information visualization technique that uses color to represent attributes of information in a two-dimensional image. Heat maps use shades or colors to differentiate values in a data set or to identify focus areas in a data set. Different colors indicate an anomaly (eg: red in a group that is mostly green), consistent colors in a group indicate a trend.

Heatmap software technologies allow users to conduct ad hoc re-grouping, filtering, searching, selecting, exporting, printing and importing from external data sources. [Commercial software] [cheap / free treemap software]

The University of Maryland has an excellent history and explanation of heatmaps and coverage of treemap software offerings. There is an extensive set of variations of how to implement heatmap visualization.

There are different types of heat maps. The two most commonly used heatmap types are treemaps and geographic (thematic) maps.