Tree maps show parts of the whole by using nested rectangles. Each rectangle is designated a size and a shade of a color. This enables you to emphasize both the importance (usually shown by size) and urgency (usually represented by color) of a data point.
• Used often for portfolio analysis to highlight similarities and anomalies.
• Usually require interactivity such as mouse-over, to read the subcategory labels for the smallest rectangles.
• This chart type is best used for analysis and exploration rather than presentation.
Sosulski, Kristen. Data Visualization Made Simple (p. 50). Taylor and Francis. Kindle Edition.