a map... of rap... in New York City. From the data visualization people at Very Small Array
The place where I found this also linked to a more international "The Rap Map", but I can't get much out of that site.
I have been following Brain Rot's serial graphical history of Hip Hop by Ed Piskor over at BoingBoing.net. Informative, sure, but I'm still not that interested in hip hop or rap.