Treemaps (sometimes called heatmaps) are one of my favorite data visualization techniques, and it has taken me a while to finally figure out how to do them. The idea is simple: Each component is represented by a rectangle whose area is proportional to the ‘weight’ or relative importance of the item. I finally did find a technical paper on the idea and have implemented it in my source code. The algorithm efficiently finds what the best dimensions should be for the rectangle keeping its length-to-width ratio as close to one as possible. The demo application reads Digg’s music news feed and draws rectangled based on the number of diggs each entry got. To really play with the application, resize the container and see the application redraw itself to respond to the change in dimensions. I think the coolest part of the code is the fact that the drawing part is fairly abstracted from the logic that computes the sizing. So to create your own ‘renderer’, all you have to do is extend the HLayoutManager and the VLayoutManager and override the draw method.
The code is released under the MIT liscense, so feel free to use it.
[Update: The latest version of the library is now on GitHub. The new version decouples the dependency on nested Sprites and gives you a lot more control on elements you'd like to lay out. Also check out some fantastic examples using the library by nicoptere]