Yes, telcos have an error of a few km. Google tells me, from another country, where exactly I came from, where exactly I went, and how (walking, driving, ...)
The accelerometer in most phones is accurate enough to detect individual footsteps. Phones also include a barometer that is sensitive enough to detect which floor of a building you are on. With dead reckoning based on accelerometers, calibrated by GPS, compass, WiFi, and barometric data, people can be located to within centimeters. Activity detection, mode of transport--ha, child's play!
If you run Android, turn off "high location accuracy". It uses all of these features.
:) I really don't care that Google knows what I'm doing. What I do find amazing is that people are usually afraid of telcos for tracking, when it's more like you have to be afraid of Google and apps like Candy Crush...
You realize that with a NSL the US government can compel Google to disclose information on anyone and that the contents of NSLs are completely secret, right? Oh yeah, and Google operates globally and no one really knows what arrangements they have with the various governments around the world.
Or even worse, arrangements with criminal and terrorist organizations, committing warcrimes all over. They now love to shoot you down with a drone based on Android High Accuracy Location Tracking, without any due process. They also love to block free travel without due process. It's called freedom (of civil rights, to block and terminate).
One of the hardest problems, a few years back, to solve was getting data to determine which traffic lane you were in. It was to provide targeted ads on billboards, that through reflection, could show different ads to people in different lanes based on "external" searches such as browsing patterns. To my knowledge the problem was not solvable using wireless telco data.
I've got a bunch of the privacy stuff on my Android phone, and even when I use Google Maps while driving I'll ask "where's the nearest grocery store" and it will regularly think I'm hundreds of miles from where I am. I can't even figure out why. It once thought I was in the ocean.
To be clear, when I am asking this, the phone has access to my location data and everything else it asks for.
Many phones manufactured after 2005 have GPS receivers built in. When the cellular phone detects that the user is placing an emergency call, it begins to transmit its location to a secure server, from which the PSAP can retrieve it. Cellphone manufacturers may program the phone to automatically enable GPS functionality (if disabled) when an emergency call is placed, so that it may transmit its location.
Phones go into an emergency mode where they transmit the gps location. The accuracy depends on factors including length of call iirc.
I believe they can then call the carrier to ping the phone to report location. Typically that happens if the dispatcher has reason to believe there is a emergency situation and the call drops.
I think the phone will notify you of this. At least it did many years ago when I called 911 for a car accident on the highway.