Creating Tree Maps
Using the Tree Map Platform
Tree maps are useful for observing patterns among groups that have many levels. Tree maps are like bar charts that have been folded over in two dimensions so that there is no unused space. Rather than drawing a single bar for each measurement, a tree map can show the magnitude of a measurement by varying the size or color of a rectangular area. Use tree maps when your data contains many categories, to visualize many groups.
Tree maps were named and popularized by Ben Schneiderman, who has an extensive Web site about the idea (http://www.cs.umd.edu/hcil/treemap-history/index.shtml
Figure 19.1 Example of a Tree Map