sfhaps:

The Geotaggers’ World Atlas: San Francisco by Eric Fischer

The different colors represent different modes of transportation: Black is walking (less than 7mph), Red is bicycling or equivalent speed (less than 19mph), Blue is motor vehicles on normal roads (less than 43mph); Green is freeways or rapid transit. Lines never looked so cool.
via http://blog.flickr.net/en/2010/05/24/beauty-in-vectors/