This is a thought experiment at best. If we ignore the privacy concerns, there is the basic practical issue that location tracking is often wildly bad and would lead to tons of false positive and negative selection of people to test. Over the years I've used a variety of Garmin watches and iPhones to track runs and walks. In areas with tall buildings or steep hills and trees all of these systems will jump around and track me as if I were superman bounding over/through buildings and city blocks from one second to the next.