If you wanted to track the movements of 150,000 tourists as they ate, drank, shopped, and “Cheese-d!” their way around New York, you wouldn’t need to hack the NYPD’s surveillance system. You could just access Flickr’s and Picasa’s public-search APIs, essentially open-air source code that lets opportunistic computer programmers like Oakland’s Eric Fischer search for and filter pictures that meet certain criteria, in this case geographic location. Above, Fischer has plotted on a map of New York every single geotagged photograph uploaded to the two photo-sharing sites over the past year. Anyone who snapped pics here for less than 30 days in a row, he reasoned, is most likely a tourist.

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