How does foursquare determine location from the browser without asking permission

Question

how foursquare determine a user location?

I'm following this question about how foursquare determines a user location from the browser. Yeah, I know about the navigator.geolocation.getCurrentPosition and it works, but it asks for a user's permission when I implement. I cleared out my browser's location permissions in chrome and firefox, but they still know where I am.

My question: How do they do this? I thought they used geoip, but their privacy statement says otherwise.

Thanks

Answer 1

Their privacy policy doesn't really say they don't use some form of geo-IP location:

We automatically receive your location when you use the Service. We use various technologies to determine location, such as location services of the applicable operating system or browser and sensor data from your device that may, for example, provide information on nearby Wi-Fi- access points and cell towers.

It's mostly tailored for the app, as you'd expect, but it's general enough to not rule out IP-based location detection.

I'd say they are using IP detection. If you visit their site with no session or cookies, and Javascript disabled, it still knows your approximate location, so they're definitely not using client-side detection, at least not entirely. Open the site through a proxy and you'll get a different city to what you get going direct, so it's safe to assume they're using the IP.