Facebook has long said that it doesn’t use location data to make friend suggestions, but that doesn’t mean it hasn’t thought about using it.
In 2014, Facebook filed a patent application for a technique that employs smartphone data to figure out if two people might know each other. The author, an engineering manager at Facebook named Ben Chen, wrote that it was not merely possible to detect that two smartphones were in the same place at the same time, but that by comparing the accelerometer and gyroscope readings of each phone, the data could identify when people were facing each other or walking together. That way, Facebook could suggest you friend the person you were talking to at a bar last night, and not all the other people there that you chose not to talk to.
Facebook says it hasn’t put this technique into practice.
“We’re not currently using location [for People You May Know],” said a Facebook spokesperson. Facebook has previously told us that it only used location for friend recommendations one time during a brief test in 2015. But several of its patents show it thinking about using location, also recommending users friend each other, for example, if they “check into the social network from the same location at around the same time.”
In the course of our year-long investigation into how the social network makes its uncannily accurate friend recommendations to users, Facebook has told us many things it doesn’t do, to ease fears about Facebook’s ability to spy on its users: It doesn’t use proxies for location, such as wi-fi networks or IP addresses. It doesn’t use profile views or face recognition or who you text with on WhatsApp. Most of Facebook’s uncanny guesswork is the result of a healthy percentage of users simply handing over their address books.