How is Google updating its Geolocation database?

Question

I understand that Google used the security kit in their Street View cars to download their wifi beacon landmark map.

But what data sources and methods do they use to detect and register new access points? Will they only download the new BSSIDs sent by my Android phones with a valid GPS fix?

I installed two new access points (one of them with dual 2.4 / 5 GHz), and for two weeks Google had a fix for them, although 290 meters from the real place. I will see if this fix will be updated over time.

I am fascinated by this, but I have not found any more details on how they do it.