The "flattening factor" measures the compression of a sphere. The notation of f is used for flattening.
The following ellipsoids come from Map Projections - A Working Manual (Snyder, 1987)and other sources. Radii may be specified more precisely than the 0.1 meter shown here.
| Name | Year | Equatorial Radius, RM meters | Polar Radius, Rm meters | Flattening factor, f | Users |
|---|---|---|---|---|---|
| Airy | 1830 | 6,377,563.4 | 6,356,256.9 | 1/299.32 | Great Britain |
| Bessel | 1841 | 6,377,397.2 | 6,356,079.0 | 1/299.15 | Central Europe; Chile; Indonesia |
| Clarke | 1866 | 6,378,206.4 | 6,356,583.8 | 1/294.98 | North America; Philippines |
| Clarke | 1880 | 6,378,249.1 | 6,356,514.9 | 1/293.46 | Most of Africa; France |
| International | 1924 | 6,378,388.0 | 6,356,911.9 | 1/297.00 | Much of the world |
| Australian | 1965 | 6,378,160.0 | 6,356,774.7 | 1/298.25 | Australia |
| WGS72 | 1972 | 6,378,135.0 | 6,356,750.5 | 1/298.26 | NASA, US Dept. of Defense |
| GRS80 | 1980 | 6,378,137.0 | 6,356,752.3 | 1/298.26 | Worldwide |
| WGS84 | 1984 - current | 6,378,137.0 | 6,356,752.3 | 1/298.26 | Worldwide |
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