I believe this data mainly comes from phones, not street view cars. There are about a million times more phones out there than street view cars, and they all have GPS and Wifi. Apple had this feature long before Apple Maps was a thing, and they didn't license Street View data from Google.

Is it related to Android though? I read somewhere/thought that it is primarily the Google Maps cars recording WiFi data and not phones). Europe wouldn't be covered at all if it was coming from the phones, right? (GDPR)

I mean, you can have a street full of iPhones - which I assume is a regular occurrence in USA, where people trust Apple - and still Google Maps on iPhone would guess well enough where you are. For example, I'm far away from the street and Google hasn't passed here recently, so my WiFi-based location is always way off (using Android). In my other home (and vacation home in another country) it's the opposite, because the cars have passed quite recently.

The story checks out so far for me... but I am kinda lazy to search for the source on this right now, so pls share if you have it.

> Europe wouldn't be covered at all if it was coming from the phones, right? (GDPR)

Which part of GDPR would prevent Google from collecting pairs of (Wi-Fi BSSID, approx lat/lon), with the consent that you gave when you set up your Android phone, and using it for their own purpose without giving it to any third party?

They give it to a third party - other chrome users. I was once in a train, and location services located me in a suburb hundreds of km away - clearly I was traveling with someone living there, using a portable/mobile hotspot. These kind of edge cases are hard to prevent (and rare), but still can lead to serious fines.

Your example doesn't demonstrate Google giving the data to other Chrome users. Making decisions based on the data is not the same as giving the data out.