The idea of offering people free Wi-Fi in exchange for their physical coordinates began at Facebook as a one-off experiment, a project by two engineers during an all-nighter in May 2012. Since then, Facebook has gradually spread what it now calls “Facebook Wi-Fi” further and further beyond the company’s corporate walls, deploying the system to cafes in Palo Alto and San Francisco and even into a line of routers made by Cisco.

The growth of Facebook’s free internet offering underscores the extent to which the social network is trying to vacuum up more and more information about its members, including their physical movements, and how valuable such data has become in selling advertising.

Intended for use in businesses like cafes, Facebook Wi-Fi asks users to “check in” at the business location using their Facebook account. Once they do, or once they click a small opt-out link, they are granted wireless internet access. The system was developed during a hackathon at Facebook’s Seattle office by engineers Mohit Talwar and Adrian Potra. After winning raucous applause at a "prototype forum" after the programming marathon, it was forwarded to top Facebook brass, who assigned a team of three at the company's Menlo Park, California headquarters to develop the idea further.

When we first wrote about Facebook Wi-Fi in November, Facebook told us the system was highly experimental, “a small test with a few local businesses” around headquarters in Menlo Park, California.

Within a few months, reports on Twitter indicated the experiment had spread to San Francisco locations of the Philz Coffee chain. We were able to use the system at the Philz location near AT&T Park and have been told it's up and running in Philz’s Castro location as well.

In May, Facebook Wi-Fi graduated beyond experiment as Cisco announced the service would be included as an optional service on its Meraki line of routers. Facebook is in discussions with other router makers to get Facebook Wi-Fi adopted more broadly, according to Facebook mobile product manager Erick Tseng.

Where Facebook Wi-Fi goes from there remains to be seen. It was impossible not to wonder if a major expansion might be in store last week, when Facebook sent out java-stained invitations to the press, inviting reporters to “join us for coffee and learn about a new product… a small team has been working on.”

But with Facebook in deals to harness grocery store purchase data and with the company having reportedly considered spending $1 billion to buy an app that shares car location data, there’s no question the social network is hungry for data on where you’re going and what you might be buying. That’s precisely the sort of siloed information internet giants like Facebook, Google, and Yahoo are increasingly being asked to use for ever-more-precise ad targeting. Given all the private location that’s shared without people even realizing it, Facebook Wi-Fi has the virtue of at least offering the user something valuable in return for her location. Which is why we won’t be surprised to see the long steady march of the system continue.