1/ Well, to answer this, sign up for the phone company's family plans designed to allow you to track your children. It's hit or miss, sometimes very accurate, sometimes not.
2/ Modern phones and towers have multiple abilities to track your location. For one thing, because of speed-of-light delay, the tower must know your distance from the tower to within 100 meters.
3/ Next, towers know which directional antenna your signal arrives on. This gives them a 120° arc within which to locate you, the closer you are to the tower, the more accurate that is, of course.
4/ Modern 4G/LTE has additional crap like phased array, multi-user MIMO, and stuff which allows the tower to get even closer. You need a modern phone for that, so they can locate a iPhone Xs better than an iPhone 5.
5/ In Modern 4G/LTE, they can also ask your phone. Phones scale their power output to reach only the nearest tower, so multiple towers can't triangulate/multilaterate your phone. But your phone can hear towers, so the phone can triangulate/multilaterate itself.
6/ So, part of the 4G/LTE protocol consists of the tower being able to ask the phone it's location. However, it typically doesn't do this all the time, only in such cases like when you place a 911 emergency call, and they need to know your location.
7/ According to the E911 regulations, mobile phone companies are supposed to be able to guarantee that most emergency 911 calls can locate you within 50 meters, or less. So it's the government driving this.
8/ However, just because they CAN get your location accurately on a 911 doesn't mean they ARE getting it accurately. Cell towers log the data needed to get cell tech working, and 911 systems log the data when such calls are placed, but a lot of the accurate stuff isn't logged.
9/ Thus, in my testing of the Family location services, sometimes it would tell me exactly which parking space in the parking lot I was parked in, and sometimes this I'd be 500 meters away from the location it thought.
10/ FYI: All my testing is with WiFi and GPS disabled, with the latest iPhones and with older feature phones.
11/ In cities, location accuracy is a problem big signals bounce around. One of the claimed benefits of 5G is that since "towers" are at the density of WiFi access points, location will finally be fixed and they'll know where you are finally.
12/ BTW, don't forget about height. All modern phones contain pressure sensors trying to figure out through atmospheric pressure readings what floor you are on. It's how fitness trackers also figure out how many floors you've climbed.
13/ Anyway, be careful with the sensationalized stories about how accurate the location was. While it CAN be that accurate sometimes, it doesn't mean it's ALWAYS that accurate. In my testing, it was about 50% scary accurate and 50% laughably way off.
