Treemap
A treemap represents a hierarchy with nested rectangles. Each rectangle's area is proportional to its value. Parent groups contain the rectangles for their children.
Read size within the hierarchy
The Product section has 400 page views: 240 for Guides and 160 for Features. The Company section has 200. Product therefore occupies twice as much area as Company.
The layout packs rectangles into the available space. Horizontal and vertical position do not act as numeric axes. Compare area, not width alone.
When a treemap is useful
Use it to show how a total is divided across groups and subgroups, such as storage by folder or sales by product family. It can fit more categories than a pie chart, though very small items may be difficult to label.
Use non-negative values with a meaningful sum. Avoid counting a parent total again as a separate child. If some categories are excluded, state that the displayed total is partial.
Know the tradeoffs
Readers find close areas harder to compare than bar lengths. Use a bar chart for a precise ranking. Large changes in values can also rearrange the layout, making comparisons across dates difficult.
Label groups and provide exact values. Color can identify a parent group or encode a second measure, but explain which it does. For the same hierarchy in rings, see sunburst chart.
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