Mapping a City's Rhythm

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Jebara is aware that the idea of tracking people's movements makes some people uncomfortable, but he insists that the data used is stripped of all identifying information. In addition, anyone who uses Citysense must first agree to let the system log her position. A user can also, at any time, delete her data from the Sense Networks database, Jebara says.

Part of Sense Networks' business plan involves providing GPS data about city activity to advertisers, Jebara says. But again, this does not mean revealing an individual's whereabouts--just where certain types of people congregate and when. For instance, Sense Networks' data-analysis algorithms may show that a particular demographic heads to bars downtown between 6 and 9 P.M. on weekdays. Advertisers could then tailor ads on a billboard screen to that specific crowd.

So far, Jebara says, Sense Networks has categorized 20 types, or "tribes," of people in cities, including "young and edgy," "business traveler," "weekend mole," and "homebody." These tribes are determined using three types of data: a person's "flow," or movements around a city; publicly available data concerning the company addresses in a city; and demographic data collected by the U.S. Census Bureau. If a person spends the evening in a certain neighborhood, it's more likely that she lives in that neighborhood and shares some of its demographic traits.

By analyzing these types of data, engineers at Sense Networks can determine the probability that a user will visit a certain type of location, like a coffee shop, at any time. Within a couple of weeks, says Jebara, the matrix provides a reliable probability of the type of place--not the exact place or location--that a person will be at any given hour in a week. The probability is constantly updated, but in general, says Jebara, most people's behavior does not vary dramatically from day to day.

Sense Networks is exploring what GPS data can reveal about behavior, says Eric Paulos, a professor of computer science at Carnegie Mellon. "It's interesting to see things like this, [something] that was just research a few years ago, coming to the market," he adds. Paulos says it will be important to make sure that people are aware of what data is being used and how, but he predicts that more and more companies are going to find ways to make use of the digital bread crumbs we leave behind. "It's going to happen," he says.