A phone won't have a complete map of cell towers and wi-fi, it can't locate itself without using GPS. Thus it's basically saying "I'm somewhere around here, th

A phone won't have a complete map of cell towers and wi-fi, it can't locate itself without using GPS. Thus it's basically saying "I'm somewhere around here, this is what I see. Where am I?". You can't send a query without providing an address to receive an answer. Sending such a query is a lot less energy intensive than GPS and it has a lot more ability to penetrate than GPS--when you're indoors it's the only game in town and I've seen occasional instances where GPS wouldn't even work inside a car unless you put the unit on the dash. A unique ID wouldn't be required for this to work but without some sort of security measure you can figure others would piggyback on your service.