In addition to this people do things to their phones that make data useless quite often. They turn off their gps, root the phone and change the clock so they can cheat at games, use location spoofing apps so they can pretend to be somewhere else on tinder. Then on top of that it can be hard to tell where people are even with gps on because being in a building screws it up. There are several solutions to that problem but nothing is perfect.