This is a tree map for the minicpan mirror, containing only the latest versions of all CPAN distributions. Within the application, you can mouse over the rectangles to see which files and folders they represent, but here I've just annotated a few interesting blocks. Somehow it feels like a city layout...
See the blog entry.
A couple of years ago I wrote MiniCPAN and GrandPerspective for my O'Reilly blog.