# Hayford ellipsoid

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Earth-approximating ellipsoid introduced in 1910

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In [geodesy](/source/Geodesy), the **Hayford ellipsoid** is a [reference ellipsoid](/source/Reference_ellipsoid) named after the American [geodesist](/source/Geodesist) [John Fillmore Hayford](/source/John_Fillmore_Hayford) (1868–1925), which was introduced in 1910. The Hayford ellipsoid was also referred to as the **International ellipsoid 1924** after it had been adopted by the [International Union of Geodesy and Geophysics](/source/International_Union_of_Geodesy_and_Geophysics) IUGG in 1924, and was recommended for use all over the world. Many countries retained their previous ellipsoids.

The Hayford ellipsoid is defined by its [semi-major axis](/source/Semi-major_axis) a = 6378388.000 m and its [flattening](/source/Flattening) f = 1:297.00. Unlike some of its predecessors, such as the [Bessel ellipsoid](/source/Bessel_ellipsoid) (a = 6377397 m, f = 1:299.15), which was a European ellipsoid, the Hayford ellipsoid also included measurements from [North America](/source/North_America), as well as other continents (to a lesser extent). It also included [isostatic](/source/Statically_indeterminate) measurements to reduce [plumbline](/source/Plumbline) divergences. Hayfords ellipsoid did not reach the accuracy of [Helmert's](/source/Friedrich_Robert_Helmert) ellipsoid published 1906 (a = 6378200 m, f = 1:298.3).

It has since been replaced as the "International ellipsoid" by the newer [Lucerne ellipsoid](https://en.wikipedia.org/w/index.php?title=Lucerne_ellipsoid&action=edit&redlink=1) (1967) and [GRS 80](/source/GRS_80) (1980).

## See also

- [Earth ellipsoid](/source/Earth_ellipsoid)

## Sources

- [Defense Mapping Agency](/source/Defense_Mapping_Agency): *Geodesy for the layman*, 1983, p. 8 [\[1\]](http://www.ngs.noaa.gov/PUBS_LIB/Geodesy4Layman/geo4lay.pdf)

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