Treemaps are also under-utilized, in my opinion! They are extremely useful visualizations for navigating hierarchical data. This was already described in Chapter 2, It's All About the Data, but I'd like to expand on what was said there:

• Good for visualizing: Hierarchical data. You can size each box in the treemap by a value in your data and navigate up and down the levels of the hierarchy interactively. They are great for collapsing large amounts of data into a single view. They are also great for setting up navigable hierarchies, so that users can sub-select parts of the data really easily.
• Don't use for: Hierarchies with lots and lots of levels; you'll get confused. Hierarchies where the amount of data in some categories is really small compared to the others (you'll end up with lots of tiny boxes that you can't interpret).
• Pros: The ability...