Shortest Route Finder
Compare the two ways of measuring a route: the great-circle path — the shortest possible distance on a sphere, the one aircraft follow — against the real road distance a car would drive, both drawn on one map with the detour factor between them.
Great-circle distance, bearing and the purple arc are computed in your browser with the Haversine formula; the road comparison comes live from the free OSRM public demo server on OpenStreetMap road data. The tool explains honestly why the two numbers differ.
How to use this tool
Type place names or “lat,lng” coordinates for the two endpoints.
The tool computes the great-circle distance, initial bearing and a live OSRM road comparison.
See how much longer the drivable road is than the shortest possible path, with both lines on the map.
What people use this tool for
See with real numbers why the New York–London great-circle arc curves north on a flat map — the path planes actually fly.
Compare the as-the-crow-flies distance with the road distance to spot inefficient routings before you leave.
Demonstrate why great-circle routes beat both rhumb lines and roads on long distances, with computed figures.
How it's calculated
Great-circle distance uses the Haversine formula and initial bearing uses spherical trigonometry on the WGS84 mean radius (6,371.0088 km); the arc is drawn with 64 spherical-linear-interpolation (slerp) points, the correct way to interpolate on a sphere. Place names are geocoded once via Nominatim. The road comparison is a live OSRM route request (driving profile); if OSRM is unreachable the great-circle results still stand and the tool says the comparison is missing.
Related tools and resources
Frequently asked questions
Why is the road distance longer than the shortest distance?
The great-circle line cuts across terrain cars can't use — oceans, mountains, private land. Roads must follow the real network, so the road route is always longer; the detour factor quantifies exactly how much longer.
Is the purple line the path a plane would fly?
Essentially yes — long-haul flights follow great-circle routes to save fuel. Real flight paths deviate for winds, airspace and safety, but the great circle is the baseline.
What is the detour factor?
Road distance divided by great-circle distance. A factor of 1.25 means the road route is 25% longer than the shortest possible path — useful for spotting inefficient routings.
What does initial bearing mean?
The compass direction to set off in from point A along the great circle. On long routes the bearing changes as you travel — this is only the starting direction.
Data sources & methodology
- OSRM — Open-source routing engine; road routes come from its public demo server.
- OpenStreetMap — The road network data OSRM routes on, and the map tiles.
- Nominatim — OpenStreetMap-based geocoder used to locate place names users type in.