Following the isochronic tube map I blogged about in January (isochronic maps basically have temporal contour lines, so that points further away in travel time are depicted as being further away on the map) here's a neat dynamically-generated map of San Francisco via boingboing.
Cabspotting is a San Francisco Exploratorium (rapidly becoming Holiday Obsession Number Two) project. As they put it in in their description:
Cabspotting traces San Francisco's taxi cabs as they travel throughout the Bay Area. The patterns traced by each cab create a living and always-changing map of city life. This map hints at economic, social, and cultural trends that are otherwise invisible. The Exploratorium has invited artists and researchers to use this information to reveal these "Invisible Dynamics."