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In the horizontal the discrete points are arranged in a two dimensional grid and hence are referred to as grid points. The grid can be regular or irregular. An example of a regular latitude/longitude grid would be where the grid points are located every 1 degree of longitude in the east-west direction and every 1 degree of latitude in the north-south direction. Each grid point is associated with an area that either surrounds the grid point or lies between the grid points. This area is referred to as the "grid box".
(In addition to using grid points, the ECMWF model (IFS) also uses an additional mathematical system, the spectral method, to represent horizontal space. This system uses a set of waves to describe variations in the horizontal. The IFS switches between spectral space and grid point space, in order to perform specific computations.)
Vertical
In the vertical, models can use levels, located at discrete points, and/or averages over layers.
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