Clarke’s Spheroid

cartography

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June 24, 2026

Quick Summary

Clarke's spheroid is an ideal oblate spheroid that represents the Earth's shape at average sea level. This concept is crucial in cartography, the science of mapmaking, which involves determining the Earth's size and shape to create accurate projections.12

An oblate spheroid is a type of ellipsoid, a closed surface where all plane cross-sections are ellipses or circles. The Earth, due to its rotation, is not a perfect sphere but an oblate spheroid, meaning it bulges at the equator and is flattened at the poles.3

British geodesist Alexander Ross Clarke developed figures for the Earth's shape in the 19th century. His 1866 determination of Clarke's Spheroid was widely used as a standard reference in geodesy, even after international standards were adopted.24

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Development of reference spheroids
The dimensions of Clarke’s Spheroid (introduced by the British geodesist Alexander Ross Clarke) of 1866 have been much used in polyconic and other tables. A later determination by Clarke in 1880 reflected the several geodetic surveys that had been conducted during the interim. An International Ellipsoid of Reference…
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The dimensions of Clarke’s Spheroid (introduced by the British geodesist Alexander Ross Clarke) of 1866 have been much used in polyconic and other tables. A later determination by Clarke in 1880 reflected the several geodetic surveys that had been conducted during the interim. An International Ellipsoid of Reference…
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Alexander Ross Clarke
…second determination (1866) became a standard reference for U.S. geodesy, even after the acceptance of other figures by the International Union of Geodesy and Geophysics in 1924.
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…second determination (1866) became a standard reference for U.S. geodesy, even after the acceptance of other figures by the International Union of Geodesy and Geophysics in 1924.
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surveying
Triangulation
…English-speaking nations is (Alexander Ross) Clarke’s Spheroid of 1866. This oblate spheroid has a polar diameter about 27 miles (43 kilometers) less than its diameter at the Equator.
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…English-speaking nations is (Alexander Ross) Clarke’s Spheroid of 1866. This oblate spheroid has a polar diameter about 27 miles (43 kilometers) less than its diameter at the Equator.
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