I'm not quite sure what you are referring to by strict background checks. But here's I think the service is used. A user initiates a call to the service requesting a ride. The service takes in the user's location and first finds the city (first tier), then the service searches and returns the georeferences in that city for ones that contain that user location. These georeferences might attached to drivers, and those drivers might be analyzed to find good drivers to send that ride request to, or they could be something like neighborhoods, where Uber would search that neighborhood for drivers. I'd guess that city specific requirements could be associated with georeferences in either tier.