GIS's Roots in Cartography

semi-major axis (a)

semi-minor axis (b)

f = 1 - b/a

For the WGS84

a = 6,378,137 m

b = 6,356,752.3 m, f=1 /298.3

The Earth is an ellipsoid, not a sphere
The World Geodetic System (WGS84) gives the "flattening of the ellipsoid as f = 1/298.257
Note dimensions in meters

< TD HEIGHT="100" WIDTH="150">View graphic version
Next slide Back to first slide