A few things to bear in mind:
- FourSquare seems to record each checkin's coordinates based on your location when you check in, so if you check in away from the venue (e.g. on your way home), the location might not be accurate.
- Distances are calculated "as the crow flies" and don't reflect actual routes between checkins.
- We don't (and indeed, can't) access your Foursquare account, only the private feed URL you give us. We calculate your travel distance and other stats on-the-fly, and no checkin data is stored.