Wednesday 5 December 2012

Spatiotemporal patterns and the dynamics of the city

One more post on GPS traces from taxis, this time from San Francisco. The video follows the origins (green dots) and destinations (red dots) of passenger trips made by taxi in San Francisco. It is based on GPS traces from 500 taxis over a full month. 

Each record contains information about location, timestamp and, crucially, whether the taxi is occupied or not. This makes it possible to mine approximations of passenger trips and therefore, their origins and destinations. Every new green dot lighting up represents the origin of a passenger trip made by taxi (the dot subsequently fades out over the next 15 minutes). Every red dot lighting up represents arrival to a destination by taxi. 

The video illustrates the tempo of the city. During the course of 24 hours (midnight to midnight), the locations of the origins and the destinations change. Areas gradually shift from being collectors of trips to being distributors and vice versa. The spatial concentration of destinations (red dots) between 7.00 and 9.00 in the business district is followed by dispersion in the evening. However, this expected pattern is not the only one observed. Other areas demonstrate their unique time profiles, which, in some cases, are dominated by relatively short peaks. 

GPS traces make it possible to identify spatiotemporal patterns that where impossible to observe until recently. As a next step, the temporal profile of each area will be compared with its land use characteristics in order to identify correlations between flows and activities.

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