> Participating in header bidding gives you data similar to what you would see from operating a popular mobile website.
A popular mobile website can only geolocate its own visitors based on IP and will have no idea what apps they have installed and what they do whenever they are not visiting that website.
The ad exchange gets information any time the users opens any of thousands of apps, without them ever interacting with the exchange.
"This device opened Grindr at this exact GPS coordinate, then Candy Crush at the church wifi, then a month later played Yahtzee for three hours near a military base in Afghanistan"
Then they package up that historical data and sell it. You can have years of location data for whatever purpose you can think of.
A thread on using this for surveillance from about a year ago:
https://news.ycombinator.com/item?id=38289337
As I commented there, while the antitrust case against Google is well-deserved, one effect of breaking their ad monopoly is opening up for even more actors to receive real-time header bidding data.
A look at the resolution of position data you can get:
https://nrkbeta.no/2020/12/03/my-phone-was-spying-on-me-so-i...
This will be correlated and joined with the geoip data from the apps without location data.