Distance & GPS
Difference between straight-line (Haversine) and real driven distance through streets.
Haversine returns the straight-line distance; routing APIs return real driven distance following streets. The gap is the "detour factor" — typically 1.3 to 1.5 in dense urban centers, 1.1 to 1.2 on highways. Professional receipts must use routed distance; using Haversine under-counts reimbursement by up to 50%.