Great Circle

Overview A great circle is formed by the intersection of a sphere with a plane that passes through the sphere's center. On Earth, great circles represent the shortest surface distance between any two points, known as the geodesic path. The equator is a great circle, as are all meridians of longitude, while parallels of latitude (except the equator) are small circles. Great circle geometry is fundamental to navigation, geodesyGeodesyGeodesy is the scientific discipline concerned with accurately measuring and representing the Earth's geometric shape..., and accurate distance measurement on the globe.

Aircraft and ships traveling long distances follow great circle routes because they represent the shortest path between departure and destination points. A great circle route between New York and London, for example, curves northward over eastern Canada and the North Atlantic rather than following a straight east-west line on a Mercator projectionMercator ProjectionThe Mercator projection is a cylindrical conformal map projection that preserves angles and shapes locally, making it.... Great circle distances are calculated using the Haversine formulaHaversine FormulaThe Haversine formula calculates the great-circle distance between two points on a sphere given their latitude and lo... or Vincenty's formulae, which account for the Earth's ellipsoidal shape for higher precision.

Great circles appear as straight lines only on gnomonic projections and as curves on most other map projections. On a Mercator projectionMercator ProjectionThe Mercator projection is a cylindrical conformal map projection that preserves angles and shapes locally, making it..., great circle routes appear as curves bowing toward the poles, while rhumb lines (constant bearing paths) appear straight but cover longer distances. This distinction is important for understanding the difference between navigational convenience and distance efficiency. Azimuthal projections centered on a point show all great circles through that point as straight lines.

GISGISGeographic Information Systems (GIS) enable users to analyze and visualize spatial data to uncover patterns, relation... software uses great circle calculations for accurate distance measurement between geographic coordinates, buffer generation on the Earth's surface, and routing applications. Telecommunications network planning uses great circles to determine optimal satellite and cable paths. Seismology maps earthquake wave propagation along great circle paths from epicenters to recording stations.