What is a great-circle distance?
A great circle is any circle on a sphere whose centre is the centre of the sphere, such as the Equator or any line of longitude. The shortest path between two points on a sphere always lies along the great circle that passes through both. This calculator uses the haversine formula on a sphere with the Earth's mean radius of 6,371 km. Because the real Earth is slightly flattened at the poles, results can differ from precise ellipsoid measurements by up to about 0.5%.
Earth's curvature
Over short distances the ground looks flat, but over thousands of kilometres the curve of the Earth matters. That is why the gold route on the globe bends: it follows the surface, and on long routes it often swings towards the poles. A path from London to Tokyo, for example, passes over northern Russia rather than the Middle East.
Latitude and longitude
Every location is written as two angles. Latitude measures how far north or south of the Equator a point lies, from 90° S to 90° N. Longitude measures how far east or west of the Prime Meridian at Greenwich it lies, from 180° W to 180° E. The coordinates under each field show the point used in the calculation; for a country this is a single reference point, not its border.
Why flat maps distort distances
A sphere cannot be flattened without stretching it. The common Mercator projection keeps angles correct for navigation but enlarges areas and distances towards the poles, so Greenland looks as large as Africa although Africa is about 14 times bigger. On such maps, the shortest route between two cities looks curved, while a straight line drawn on the map is actually longer.
Geographical distance versus travel routes
The figure shown is a straight path over the surface, ignoring mountains, borders, roads and airspace. Real journeys are longer: roads follow terrain, ships go around continents, and flights follow air corridors, winds and restricted zones. GeoCrown does not estimate travel times or transport routes. For more context, see Explore & Learn.
Coordinates come from GeoCrown's country and city data. Reference: Sources.