Graffiti Archaeology

I've always been interested in graffiti as there's been plenty of it here in Flint. I often wish I could have snapped pictures of “the block” near my old high school as it has changed over the years. The block is a wall that seems to serve no other purpose than having been unofficially designated for graffiti. Needless to say, it has been painted a great many times (once or twice by yours truly). This cool site, Graffiti Archaeology is a project devoted to the study of graffiti-covered walls as they change with time. Most of the pictures have been taken in San Francisco by many different photographers from the late 90's to present day. This site itself is beautiful and dynamic. It presents archives of the artwork in the form of a time line complete with dates.
Related links:
Art Crimes
Nozzles
Graffiti Archaeology ala'Flicker