911 dispatcher here

When you call 911 from a cell phone we get an approximate location from you phone.

This isnt a gps location from you phone, it’s based off of triangulation from nearby cell towers. Your phone sends a signal to the nearest towers and times how long it takes to get a reply, which can tell about how far from the tower you are, which basically draws a big circle around the tower, basically saying “they’re probably somewhere near the edge of this circle”

When it hits off of several towers, it narrows it down to “they’re probably somewhere in the area where these circles overlap” It then gives us some latitude and longitude coordinates and a confidence factor (which is basically "they’re within X meters of that point)

Depends on how many towers, signal strength, whether you’re inside, outside, surrounded by tall buildings, and probably crazy stuff like sunspot activity, weather, etc. that location can be pretty damn good or basically useless (I’ve seen it within 2 meters and I’ve seen it in the thousands of meters, usually we can get it down to within about 300 meters, which we consider to be a good enough confidence factor to work with if we have absolutely nothing else to go on.)

The term “ping” is pretty common in networking as basically a measure of the time it takes to send and receive a signal, it originally comes from sonar which uses an actual pinging noise and listens for the echo to bounce back. In our line of work, we tend to use ping to refer to the location data we get as “a ping” or as a verb to obtain that data “to ping a phone”

We can also request the phone company ping a phone for us if we’re no longer on the line with the caller.

Some combinations of phone hardware, cell network capabilities, and what kind of capabilities the dispatch center have do allow for actual GPS locations from the phone’s GPS hardware which is more accurate, but that’s not everywhere yet,and for the most part our bread and butter is still cell tower triangulation.

In simpler terms “Officers were to the place her phone her phone was traced to.” Or as a lot of my callers like to put it “they GPS’d her phone”

And on that note, if I can go off on a little tangent, I’d like to circle back to the confidence factor I mentioned earlier. That’s why we can’t “just gps your phone” and ask a few questions to make sure we’re sending help to the right place. Even if they had a very good ping, say 10 meters, that could still put the caller in maybe a dozen or so different apartments in that complex (and the computer is only ever about 90% sure of that ping, it hasn’t failed me dramatically yet, but the possibility is there that something isn’t working right somewhere between your phone and my computer) and if the ping drops on say a high rise office or apartment building, we only have latitude and longitude, we have no clue which floor you’re on, 10 meters could be dozens or hundreds of units across however many floors that would need to be checked.