Tree Maps are much more tree-like than Tree Diagrams. Here is another great “R” project from FlowingData blog.
Back in 1990, Ben Shneiderman, of the University of Maryland, wanted to visualize what was going on in his always-full hard drive. He wanted to know what was taking up so much space. Given the hierarchical structure of directories and files, he first tried a tree diagram. It got too big too fast to be useful though. Too many nodes. Too many branches.
The treemap was his solution. It’s an area-based visualization where the size of each rectangle represents a metric since made popular by Martin Wattenberg’s Map of the Market and Marcos Weskamp’s newsmap.
See SmartMoney’s live-updating Treemap of the stock market. (Health care and energy are big movers right now.)