I found that my non-GPS iPad can show my location on apple maps from picking up WiFi signals. Apparently, Apple has mapped WiFi routers around the world, and stores them in an iDevice even if you can't connect to them! It's both creepy and useful.
May store a few locally I suppose but most on a cloud.
WiFi device mapping is I suspect why we have Street View. Google didn't drive camera cars round every (approx) street on the planet to take nice photos. They drove the cars round to collect the location of WiFi devices. The cameras and Street View were a side effect.
1. Before Street View became available where I was living I saw a camera car driving slowly about the neighborhood. I arranged for it to pass me three or four times by walking along various paths. A year later, we have Street View. I look and ??? I am not there? I eventually look at every frame that I think I might be in, say about 20, and I am visible in exactly one. I also notice that the weather differs between frames. The activity differs. Truck unloading building materials in one and absent in the next.
Conclusion the camera car had made many passes to get the Street View images and then 'random' images had been selected from the result. I forget now but it was three or four passes I think.
This all puzzled me greatly. WHY!?
2. The whistleblower. It was in the press that google were in trouble. They were hacking people's email! This was about 10 years ago. The Camera cars were driving about running a WiFi Packet Sniffer and storing all of the captured frames. Some of these frames contained unencrypted data. Say email, passwords, and they were storing that too.
WTF!
This was them collecting the WiFi data they wanted to use for mapping purposes. They vacuumed up the unencrypted data too. They only needed the MAC addresses but the engineer decided to store everything.
3. So now it all adds up. To do location based on WiFi you need to do at least three passes to try to identify which of the WiFi nodes are FIXED and which are things like phones which would not be reliable for location purposes.
There are other companies that have collected similar WiFi data and they sell it.