Well, this sounds like potentially a pretty big deal. Facebook is using smartphone location data to recommend new friends to users, which suggests many possible privacy invasions. This is also a technique NSA uses to track surveillance targets.
"Thanks to tracking the location of users' smartphones, the social network may suggest you friend people you've shared a GPS data point with, meaning your friend suggestions could include someone whose face you know, but whose name you didn't until Facebook offered it up to you," writes Kashmir Hill at Fusion.
From her report:
"People You May Know are people on Facebook that you might know," a Facebook spokesperson said. "We show you people based on mutual friends, work and education information, networks you're part of, contacts you've imported and many other factors."
One of those factors is smartphone location. A Facebook spokesperson said though that shared location alone would not result in a friend suggestion, saying that the two parents must have had something else in common, such as overlapping networks.
"Location information by itself doesn't indicate that two people might be friends," said the Facebook spokesperson. "That's why location is only one of the factors we use to suggest people you may know."
Facebook has gotten more aggressive in its use of smartphone location data in the last year, tracking which stores you go to in order to tell advertisers if their online ads worked and letting advertisers use your phone's location to geotarget you with ads. But until now, most people didn't realize that Facebook was also tracking their phone's location to suggest friends to them.
There are all sorts of positive and abusive scenarios one could imagine with location-based social network suggestions, some of which Kashmir details in the article.
In a 2015 report titled "Why Does Facebook Keep Suggesting You Friend Your Tinder Matches," Motherboard questioned exactly how Facebook seemed to be figuring out out with whom its users were going out on Tinder dates.
"The report was ultimately inconclusive as experts said that data from Tinder doesn't flow back to Facebook, but it may well have been location-based."