Using data from the location-based social network provider Gowalla, researchers at Rensselaer Polytechnic Institute in New York found people tend to move in groups of friends and that two people chosen at random at a specific event, like a concert or at a particular store, are unlikely to be friends.
The findings, although seeming common sense, could have an impact on predictions of how people move, which could affect application that rely on such predictions for emergency planning, infrastructure development, communications networks and disease control, researchers said.
"The ramifications are extremely important because if we assume that people are moving randomly, we are wrong, and therefore we will not be prepared for what people actually do," Rensselaer computer scientist Boleslaw Szymanski said. "Where you live really matters: Most of your friends are concentrated in the place where you live, and as the distance increases, this concentration rapidly drops."
The study suggests still form friendships based on personal interactions despite the rise of social media in the digital age, the researchers said.
"Even though, thanks to the Internet, you can be friends with anyone on the planet, the likelihood that a person will be friends with someone in a distant location chosen at random is far lower than the likelihood that this person will be friends with someone who lives in close proximity," Rensselaer graduate student Tommy Nguyen said.
As distance increases the likelihood of friendship between two people decreases, so 80 percent of a particular person's friends live within 600 miles of that person's home, the study found.
"Proximity creates a strong boundary for who will be your friends," Nguyen said.