City folk may feel like they're constantly at the office, but they actually spend the largest portion of their traveling time visiting friends for fun. That's according to a new study that used anonymized cell phone data to figure out who people's closest contacts were, as well as where people go throughout the day. It's one of the first to combine these two kinds of information about people, the study scientists say, and the results are cheering, if unsurprising.
"We've presented a model where some choices that people make where to move are based on social behavior—where your contacts are going—and it turns out that people, on average, make choices based on these social conditions about 20 percent of the time," says Jameson Toole, a doctoral student in engineering systems at MIT, who led the study. In other words, people aren't robots who only shuttle between home, work, and other responsibilities. Nor do they only keep in touch with friends over the phone. Those they call the most, they visit with the most. This effect held true in three cities Toole and his colleagues studied, in Europe and South America.
"If you have a model that only takes into account distance, you're going to miss 20 percent of all the choices people make."
Besides re-affirming that people are willing to travel to hang out with friends, the study could help city planners build more efficiently. When developing public-transportation systems, city planners must take into account what the demand will be on their new system. To do that, they use mathematical models that incorporate some known patterns about how urbanites move. People are more likely to stay close to home than to wander afar, for example, and they often return to places they've visited before. Such models don't usually take people's relationships into consideration, however. Toole's research, which was published last week in the journal Interface, shows that's a mistake. "If you have a model that only takes into account distance, you're going to miss 20 percent of all the choices people make," he says.
The research also underscores just how much about human behavior scientists are able to uncover from cell phone data. Toole and his colleagues got access to the data they needed through an agreement between MIT and different mobile operators, and basically used two datasets to pinpoint the extent to which social relationships affect people's travel patterns. The first set included which cell phone towers different phones pinged throughout the day, as people called and texted; the second showed which people called each other the most.
From that, Toole and his colleagues discovered that people who contact each other the most also tend to have similar travel patterns—a fact that allowed for the researchers to then predict people's travel patterns, based on their frequent contacts. This effect held true even for people two degrees of separation away from each other; friends of friends of friends have more similar travel patterns than strangers do.
Of course, the underlying assumption of this research is that people's true constant companions aren't their friends, but their phones.