Check out this Twitter Map of Ann Arbor, @dokas turned me on to. Can you spot the high schools?
Also cool: go a little east and find Detroit Metro. The terminal buildings are really clearly visible: http://www.mapbox.com/labs/twitter-gnip/brands/#14/42.2075/-83.3568
Wow. Pretty cool. Also interesting: the Detroit/suburbs divide is easily observed through iOS versus Android users.
This shows pretty clearly that people Tweet a lot in their cars, especially when stopped at intersections, doesn't it?
The metro Detroit area delineation is incredibly stark. Nation-wide you can immediately pick out college campuses and airports because they’re universally hot red pockets, DTW, MSU, and Oakland University are good examples. And you have to love how unususually cleanly the boundaries of Las Vegas are.
Also interesting:* there seems to be a hot spot of Blackberry users in mid/lower Manhattan* Las Vegas shows a similar iPhone/Android split as Detroit, though not quite as stark* nobody in Spain uses iPhones, apparently
I like how you can see the Stadium is relatively clearly delineated and even little Crisler next to it.