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A "true circumnavigation" of Earth is defined, in order to account for the shape of Earth, to be about 2.5 times as long, including a crossing of the equator, at about 40,000 km (25,000 mi). [24] On the flat Earth model, the ratios would require the Antarctic Circle to be 2.5 times the length of the circumnavigation, or 2.5 × 2.5 = 6.25 times ...
The simplest model for the shape of the entire Earth is a sphere. The Earth's radius is the distance from Earth's center to its surface, about 6,371 km (3,959 mi). While "radius" normally is a characteristic of perfect spheres, the Earth deviates from spherical by only a third of a percent, sufficiently close to treat it as a sphere in many ...
as the shape of the geoid, the mean sea level of the world ocean; or; as the shape of Earth's land surface as it rises above and falls below the sea. As the science of geodesy measured Earth more accurately, the shape of the geoid was first found not to be a perfect sphere but to approximate an oblate spheroid, a specific type of ellipsoid.
The prolate spheroid is the approximate shape of the ball in several sports, such as in the rugby ball. Several moons of the Solar System approximate prolate spheroids in shape, though they are actually triaxial ellipsoids. Examples are Saturn's satellites Mimas, Enceladus, and Tethys and Uranus' satellite Miranda.
Projection construction is also affected by how the shape of the Earth or planetary body is approximated. In the following section on projection categories, the earth is taken as a sphere in order to simplify the discussion. However, the Earth's actual shape is closer to an oblate ellipsoid. Whether spherical or ellipsoidal, the principles ...
The Kissing Number Problem. A broad category of problems in math are called the Sphere Packing Problems. They range from pure math to practical applications, generally putting math terminology to ...
The Klein bottle immersed in three-dimensional space The surface of the Earth requires (at least) two charts to include every point. Here the globe is decomposed into charts around the North and South Poles. In mathematics, a manifold is a topological space that locally resembles Euclidean space near each point.
The geoid is often expressed as a geoid undulation or geoidal height above a given reference ellipsoid, which is a slightly flattened sphere whose equatorial bulge is caused by the planet's rotation. Generally the geoidal height rises where the Earth's material is locally more dense and exerts greater gravitational force than the surrounding areas.