Thank You Facebook for the Opt-in!!!

Today Facebook begins rolling out a new opt-in feature called Nearby Friends. It lets friends see approximately how far away you are from them, and you can share your exact, on-going location with them for a limited time. While it’s sure to stir privacy concerns, Nearby Friends could get people spending more time with friends in the real-world instead of online as it hits iOS and Android in the US in the coming weeks.

Below is a deep analysis of how Nearby Friends works, how it was built, its privacy implications, how it impacts the competitive landscape, and its long-term opportunities for Facebook. But here’s the older  version:

Nearby Friends was built by the Glancee location sharing app team led by Andrea Vaccari that Facebook acquired in 2012. It adds a list of nearby friends to Facebook’s iOS and Android apps. It will also send notifications if you come within a short distance of a friend, and if someone shares their precise location with you you’ll see it on a map.

Vaccari tells me “the idea is to make it really easy to discover when someone is around you, and meet up and spend time together.” It wants to facilitate those serendipitous meetups where you run into a friend and end up having a meal or hanging out together. It’s a meatspace manifestation of Facebook’s mission to connect people, and a rebuttal to criticism that Facebook isolates us.

The feature could spell trouble for other location sharing apps like Foursquare and Google Latitude that haven’t reached ubiquity, as Facebook has built it into its core iOS and Android apps that have enormous userbases. It could also challenge the friend-gathering features of Highlight, Banjo, Sonar, Connect, and more startups. [Disclosure: I advise an unlaunched location sharing startup] Leaving Nearby Friends on will cause some battery drain, but not as bad as some other location apps, according to Facebook.

As for privacy, Nearby Friends is opt-in so you can ignore it and never have to use it if you don’t want to. It’s only available to people over 18. It uses a reciprocal privacy model so you can only see your proximity to friends if you both have it turned on, and you can only see someone’s exact location if they purposefully share it with you. While you can select the specific list or group of friends you want to share your proximity with, many people may simply keep this visible to all their friends — a very wide net. This and how easy it is to forget to turn off Nearby Friends could lead to inadvertent “oversharing”. But used properly, Nearby Friends could help people gather with more friends for Tuesday dinners, Friday night parties, or Saturdays in the park.