Artist and Masters student in the Media Arts and Technology department at the University of California, Santa Barbara, Reza Ali has been showcasing different visualization experiments on his blog.
The images shown here are from his latest project created for one of his classes at UCSB. Using one year's (2008) transaction data from the Seattle Public Library, Ali mapped the number of times each Dewey item (these include books, CD, DVD, etc) was either checked in or checked out from the Library, in order to understand some interesting habits and trends. As you can see from the piece, the "Arts" category clearly dominates over the others, and the largest child of that node is "Music". Although it's still work in progress, this visualization sketch is quite promising.