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Cabspotting
Every Yellow Cab taxi in San Francisco is equipped with a GPS device which broadcasts its position once a minute, for dispatches. There are about 400 of these represented in Cabspotting, a Stamen collaboration with Scott Snibbe and The Exploratorium.
This map shows the speed of the overall taxi system as the cabs drive around town. It maps not only the shape of the city in response to changing conditions (in this case, the morning rush hour), but also shows the flow of time as the city goes about the beginning of its' day.