- Tetrad (unit of area)
A tetrad is an area 2km x 2km square.
The term has a particular use in connection with the British
Ordnance Surveynational grid, and then refers to any of the 25 such squares which make up a standard hectad. These are numbered from A to Z according the "DINTY" system as shown in the grid below (taking its name from the second line).
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