A heat map is a two-dimensional representation of data in which values are represented by colors. A simple heat map provides an immediate visual summary of information. More elaborate heat maps allow the viewer to understand complex data sets.
In the United States, many people are familiar with heat maps from viewing television news programs. During a presidential election, for instance, a geographic heat map with the colors red and blue will quickly inform the viewer which states each candidate has won.
In this election heat map, the red states are Republican and the blue states are Democrat.
Another type of heat map, which is often used in business, is sometimes referred to as a tree map. This type of heat map uses rectangles to represent components of a data set. The largest rectangle represents the dominant logical division of data and smaller rectangles illustrate other sub-divisions within the data set. The color and size of the rectangles on this type of heat map can correspond to two different values, allowing the viewer to perceive two variables at once. Tree maps are often used for budget proposals, stock market analysis, risk management, project portfolio analysis, market share analysis, website design and network management.
This heat map for a student's personal budget illustrates two variables. The size of the rectangles illustrates an expense's percentage of total expenditures. The color represents whether or not the student feels the expenditure can be changed (blue) or can't be changed (red).
There can be many ways to display heat maps, but they all share one thing in common -- they use color to communicate relationships between data values that would be would be much harder to understand if presented numerically in a spreadsheet.
See also: data visualization