A Gaussian grid is used in the earth sciences as a gridded horizontal coordinate system for scientific modeling on a sphere (i.e., the approximate shape of the Earth). The grid is rectangular, with a set number of orthogonal coordinates (usually latitude and longitude).
At a given latitude (or parallel), the gridpoints are equally spaced. On the contrary along a longitude (or meridian) the gridpoints are unequally spaced. The spacing between grid points is defined by Gaussian quadrature.[further explanation needed] By contrast, in the "normal" geographic latitude-longitude grid, gridpoints are equally spaced along both latitudes and longitudes. Gaussian grids also have no grid points at the poles.
In a regular Gaussian grid, the number of gridpoints along the longitudes is constant, usually double the number along the latitudes. In a reduced (or thinned) Gaussian grid, the number of gridpoints in the rows decreases towards the poles, which keeps the gridpoint separation approximately constant across the sphere.