hikermor, all modern cellphones with GPS report their location regularly to the carrier. If there are no GPS coordinates for any reason (or if the carrier doesn’t have the data any more), most of the time the carriers can tell which cell tower the phone was connected to, reducing the area to search. The police can ask the carrier to “ping” a specific cellphone if they’re looking for someone, for the same sort of result, if the phone is turned on and in range of a tower. If more than one tower is in range, the “ping” can result in a much better location estimate.