At least some, if not the majority, is likely derived from the IP address used in the ad bidding process.
> Franaszek also says that “a significant amount of this geolocation dataset appears to be inferred by IP address to geolocation lookups, meaning the vendor or their source is deriving the user's geolocation by checking their IP address rather than by using GNSS [Global Navigation Satellite System]/GPS data. That would suggest that the data is not being sourced entirely from a location data SDK.”
> Franaszek also says that “a significant amount of this geolocation dataset appears to be inferred by IP address to geolocation lookups, meaning the vendor or their source is deriving the user's geolocation by checking their IP address rather than by using GNSS [Global Navigation Satellite System]/GPS data. That would suggest that the data is not being sourced entirely from a location data SDK.”