The recently presented academic paper at the WWW 2009 Conference from a group of computer science academics from Cornell University investigates the collection of roughly 35 million geotagged photos collected from Flickr, uploaded by more than 300,000 users. Their approach used in Mapping the World's Photos [www2009.eprints.org, PDF] combines content analysis based on text tags and image data with structural analysis based on geospatial data. While individual users of Flickr are simply using the site to store and share photos, their collective activity reveals a striking amount of geographic and visual information about the world.
For instance, their findings show that the Fifth Avenue Apple Store, which opened in May 2006, is more popular than many other well-known tourist sites such as St Paul's Cathedral in London, the Reichstag in Berlin and the Washington Monument in the US capital.
Interesting visualizations include diagrams for Manhattan and the San Francisco Bay area that illustrate the movement of photographers by plotting the geolocated coordinates of sequences of images taken by the same user, sorted by time, for which consecutive photos were no more than 30 minutes apart. "The figures are striking in the amount of detail they reveal about these cities. For example, one can clearly see the grid structure of the Manhattan streets, caused by users traveling and taking photos along them. The Brooklyn Bridge, in the lower center of the figure, is clearly visible, as are the Manhattan and Williamsburg bridges just to the north. One can even see the route of the ferries that take tourists from Lower Manhattan to the Statue of Liberty".
Another figure shows maps of representative images for the top landmarks in each of the top 20 North American and European cities. It raises the intriguing possibility of an online travel guidebook that could automatically identify the best sites to visit on one's next vacation, as judged by the collective wisdom of the world's photographers.