In Box

Picture (Im)perfect

A picture may be worth a thousand words. But, as it turns out, it takes almost 100 million pictures to make a map.

A picture may be worth a thousand words. But, as it turns out, it takes almost 100 million pictures to make a map.

The inventive engineers at Flickr — a popular Web site that allows users to upload and share photos online — have discovered a way to harness the data provided by their millions of users to create a constantly changing picture of the world itself.

When a user uploads a photo onto Flickr, he or she can pinpoint, or "geotag," the location where that photo was taken on an interactive map. GPS-enabled camera phones, such as Apple’s iPhone, can do this automatically. Flickr then uses these coordinates to create a "Where on Earth" ID for the photo that includes the neighborhood or town where it was taken, right up to the continent, a process known as reverse-geocoding. The actual content of the photo itself is irrelevant; it’s simply being used for its geographical data.

With 90 million geotagged photos and counting, the company’s development team realized that these locations could be plotted on a map to create an outline.

Not all locations are equally easy to plot. "Within the first few weeks [of geotagging] there were probably enough photos to map San Francisco," says Flickr’s Dan Catt, the senior engineer spearheading the project. But, he says, "there are still places in the world," such as the upper reaches of North America, "that we don’t have enough photos to do." It takes about 10,000 photos for Flickr to map just one location.

Reverse-geocoding is also a lot harder than it sounds. Attendees at a 2007 technology conference in San Diego uploaded their photos only to see them tagged as being taken at the San Diego County jail. Flickr allows users to correct the geographical data that the company’s software provides, but that creates its own set of problems. London residents, for instance, might have conflicting ideas about where Soho ends and Covent Garden begins.

For now, Catt considers the maps a "cool side project," but he hopes that by publishing the maps on its site, Flickr can "give people back" the ability to define their surroundings and trace how these definitions change over time. "Most of the data we have for Where on Earth comes from government sources. That doesn’t always correspond with what people are seeing on the ground," he says. Geography, in other words, just became user-generated.

 Twitter: @joshuakeating

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