Foursquare has measures in place to prevent people from gaming the check-in system--to keep people from faking check-ins and gaining badges and mayorships that

Foursquare has measures in place to prevent people from gaming the check-in system--to keep people from faking check-ins and gaining badges and mayorships that they didn't earn. From what I've gathered, they collected this information originally to prove that someone was really at the location where they claimed to be.