Oh, it's okay! See, gchat gets saved in logs the way that emails do, so they're also searchable by google's personalized search algorithms. Also, if your phone is in anyway listed on Google or FB or any social media sites, they can probably cross link which cell towers your phone signal bounces off of? And finally, different social media sites and Google analyze your social network compared to what they can glean from your physical location.

However, finally, in terms of FB asking you if you were from Cambridge when you were in Oxford, since areas like that tend to be shit in terms of reliably geolocating your IP ping, they tend to extrapolate to the nearest town. If you'd reloaded, it probably would have asked you if you were from X town/city relatively nearby as well.

Sorry, I'm American and marginally affiliated with intelligence/security stuff, so I'm a bit less scared than most, mostly by way of a.) I'm resigned to its omnipresence and b.) entertained by its real life fallibility. :D