Boundaries uses Flickr geotagging data to draw local area boundaries on a map. It’s creator, Tom Taylor, says:
Flickr understands that places are more than unique geographic identifiers; that they are mental models people use to identify with location. Moreover, they are fluid and opinionated, varying based on a number of parameters such as context, ambition and personal background. In true wisdom of the crowds style, Flickr use the combined selections of their thousands of photographers to compute the shape of these places.
I think it’s a wonderful idea. Tom has several other fun projects, including the Flickr game Noticings, and a handy micro-printer you could use for to-do lists or hyperlocal news print outs. He also has a talk up on http://www.dolectures.com/ where he explores more ideas.