Tourists pondering how to spend their time in a large city could one day get help from a tool developed by researchers at Yahoo. It draws on the database of millions of photos uploaded to the site Flickr to generate detailed itineraries of what sites to visit, and in what order.

"If I have two days to fill in Rome, say, the current state of the art is that I have to spend hours reading websites like Yahoo Travel and looking at online maps to come up with even a simple itinerary to fit the time I have," says Munmun De Choudhury, who worked on the project with colleagues from Yahoo's research labs in New York and Haifa, Israel, and is now at Arizona State University, in Tempe. "We thought, why not use the crowd's wisdom?"

The tool works for five cities: Barcelona, London, New York, Paris, and San Francisco. To inform its suggestions, it extracted tourists' movements between attractions in those cities from millions of photos uploaded to Flickr over three years.

Geolocation data and the tags added by users were used to determine and locate which attractions each user had visited, with reference to lists of attractions in the cities sourced from Yahoo Travel and Lonely Planet; the timestamps revealed how much time was spent at each attraction and how long it had taken to travel between them. Snaps from nontourists were excluded by only considering photos covering a span of time in a city shorter than a few weeks. Although the dataset used is not public, it would be possible to reproduce everything the tool does using the Flickr public application programming interface, says De Choudhury.

De Choudhury and colleagues developed a simple Web interface that can be used to automatically generate an itinerary to fill a specific number of days in a city. The Flickr data is used to fill the time available with visits to the most popular attractions and to specify the amount of time that should be spent at each. The order of visits is chosen to minimize travel time.

The quality of the results was tested by more than 450 users of Amazon's Mechanical Turk site--a platform for paying large numbers of people to perform relatively simple tasks. To ensure that the people doing the judging knew something of the city in question, a screening step asked them to identify a photo of a relatively minor attraction from each city. For example, a photo of Pont Neuf was shown for Paris.