It’s Thursday afternoon, and I’m on the eighth floor of a nondescript building in the Flatiron District, sitting across from Foursquare cofounder Dennis Crowley. He pulls out his phone to show me an unreleased, nameless game that he and his skunkworks-style team Foursquare Labs have been working on. Think Candyland, but instead of fantasy locations like Lollipop Woods, the game’s virtual board includes place categories associated with New York City neighborhoods. There’s a Midtown Bar, a Downtown Movie Theatre, Brooklyn Coffeeshop, Uptown Park, and so on.

As in Candyland, you move your game piece forward by drawing cards. But in Crowley’s version, the cards are the habits and locations of real people whose data has been turned into literal pawns in the game. Foursquare knows where their phones are in real time, because it powers many widely used apps, from Twitter and Uber to TripAdvisor and AccuWeather. These people aren’t playing Crowley’s game, but their real-world movements animate it: If one of them goes into a bar in midtown, for example, the person playing the game would get a Midtown Bar card.

Crowley tabs to a different part of the game, and dozens of first names and generic cartoon avatars pop up on the screen beneath the header “Brooklyn Roasting Company,” a real cafe on the first floor of the building we’re in. “Downstairs in the cafeteria there are 40 people,” Crowley says, thumbing through the list. “These are the people that are there. These are not their names. And this is not what they look like. These are [their unique advertising] IDs that we turned into a fake name and a fake avatar.”

He taps on one profile, called “Harry,” and a pie chart pops up that details the habits of the real person associated with that advertising ID. “Harry spends a lot of time in Midtown, sometimes goes to parks, and rides the subway,” Crowley says, looking over the data Foursquare has assembled from the person’s use of popular apps and geotagging services. “I can say I want Harry to be on my team. And now that Harry is on my team, everywhere that ‘Harry’ goes generates a card for me.”

This nameless game wasn’t the reason I was talking to Crowley—it’s still at least a year away from being anything other than an internal prototype, he says. But it speaks to the almost incomprehensible vastness of Foursquare’s data empire.

Ask someone about Foursquare and they’ll probably think of the once-hyped social media company, known for gamifying mobile check-ins and giving recommendations. But the Foursquare of today is a location-data giant. During an interview with NBC in November, the company’s CEO, Jeff Glueck, said that only Facebook and Google rival Foursquare in terms of location-data precision.

You might think you don’t use Foursquare, but chances are you do. Foursquare’s technology powers the geofilters in Snapchat, tagged tweets on Twitter; it’s in Uber, Apple Maps, Airbnb, WeChat, and Samsung phones, to name a few. (Condé Nast Traveler, owned by the same parent company as WIRED, relies on Foursquare data.)

In 2014, Foursquare launched Pilgrim, a piece of code that passively tracks where your phone goes using Bluetooth, Wi-Fi, GPS, and GSM to identify the coffee shop or park or Thai restaurant you’re visiting, then feeds that data to its partner apps to send you, say, an offer for a 10 percent off coupon if you leave a review for the restaurant. Today, Pilgrim and the company’s Places API are an integral part of tens of thousands of apps, sites, and interfaces. As Foursquare’s website says, “If it tells you where, it's probably built on Foursquare.”

Ostensibly, the reason I met with Crowley was to talk about Hypertrending, a temporary feature Foursquare is rolling out for this year's South by Southwest conference that the company announced Friday afternoon. It’s a map of the Austin area that shows the location of all the people with smartphones Foursquare can track, in real-time. The app anonymizes and aggregates the data so that people’s locations aren’t shown individually, but in clusters. Crowley says that’s to protect user privacy. a

“We're not sure if it's the responsible thing or not to have a view like this in the phone yet,” Crowley says. “I don't know how people will react to seeing a heat map in real time of where all the phones are. I can imagine some people would be like, ‘That's the coolest thing!’ And I can imagine some people would be like, ‘That's the creepiest thing!’”

He says this tension between creepy and cool is part of the reason Foursquare is only testing the feature at SXSW. It is only available to users in Austin and will “self-destruct” in two weeks once the festival has ended. “Part of the exercise is showing this to the innovators and creative types that are down there and [having them] help us think through and talk through what are we doing here, what should we do next,” Crowley says. If the reception is positive, Foursquare could turn the tech into a service that developers could query to build something similar.

Priya Kumar, a privacy researcher and tech ethicist, says Foursquare should have been more respectful of users before rolling out a potentially controversial feature like Hypertrending. “Foursquare and the team that created this feature didn't think about [whether] their use of this data fits the context in which the users provided it,” she says. “They should have gone back to users and let them opt in, or talked to civil society researchers who could give [Foursquare] insight on that before they even created the feature.”

Most companies that collect user data on Foursquare’s scale aren’t too keen on letting people know how much information they’re sharing. It’s understandable; people generally don’t react well to the realities of the big-data-powered world they’ve unwittingly opted into. But with Hypertrending, Foursquare takes a step in that direction anyway.

“This is the real-time movement of people that we know about, phones that we know about,” Crowley says. “And so I want to get a read on how people feel about that in general. Are they into this? Are they curious? Do they want to see what's next? Or are they like, ‘Hell no. They need to step away from this’?”

There’s an easier way, Kumar says. “If you do your due diligence before you design a feature, then maybe there's a way to envision [it] without feeling like you may have already crossed the 'creepy' line.”