Why Flight Routes Curve on a Map
Updated November 10, 2026
The shortest path between two points on a globe is an arc of a great circle. Drawn on a flat map, that arc bends toward the nearer pole, which is why a flight from Seoul to New York appears to curve up over Alaska and northern Canada.
Great circles
A great circle is any circle on a sphere whose centre is the centre of the sphere. The equator is one; so is every line of longitude paired with its opposite. Between any two places there is one great circle, and the shorter arc of it is the shortest possible route over the surface.
Stretch a string between two cities on a globe and it lies along the great circle. Do the same with a straight ruler on a flat map and you get a different, longer path, because the map has stretched the globe.
What it means on this map
- Lines between distant stops are drawn as great-circle arcs, so long east-west routes in the northern hemisphere bow north and those in the southern hemisphere bow south.
- Short hops look straight, because over a few hundred kilometres the arc and the straight line are almost the same.
- A route that crosses the Pacific leaves one edge of the map and re-enters at the other. The line is split at the 180° meridian.
- Routes along the equator, and routes that run due north or south, are straight on the map.
How distance is calculated
Distance between two stops is the length of the great-circle arc, calculated with the haversine formula and a mean Earth radius of 6,371 km. It is accurate to within about 0.5% of the true distance over the slightly flattened Earth.
| Route | Great-circle distance |
|---|---|
| Seoul to Tokyo | about 1,150 km |
| London to New York | about 5,570 km |
| Tokyo to Los Angeles | about 8,800 km |
| Seoul to New York | about 11,000 km |
| Sydney to London | about 17,000 km |
Why real journeys are longer
Aircraft follow airways, avoid closed airspace and ride or dodge jet streams, so a flown route is typically a few percent longer than the great circle. Roads and railways wind around mountains and coastlines and can be 20 to 40% longer than the straight-line figure. The total on your statistics is best read as a lower bound.
Try it on your own map
Questions and answers
- Why do flights from Asia to North America go so far north?
- Because that is the shortest way. On a globe, the direct line between East Asia and the eastern United States passes near the Arctic. It only looks like a detour on a flat map.
- Is the distance on my map the same as my airline miles?
- Close. Airline mileage is usually based on great-circle distance between airports, so the two differ mainly by how far your stop's city centre is from the airport.
- What is the longest possible distance between two places?
- About 20,000 km, half the circumference of the Earth. Two points that far apart are antipodes, exactly opposite each other on the globe.