Tetrad (area)
A tetrad is an area 2 km x 2 km square. The term has a particular use in connection with the British Ordnance Survey national grid, and then refers to any of the 25 such squares which make up a standard hectad.[1]
Tetrads are sometimes used by biologists for reporting the distribution of species to maintain a degree of confidentiality about their data,[2] though the system is not in universal use.[1]
The tetrads are labelled from A to Z (omitting O) according to the "DINTY" system as shown in the grid below, which takes its name from the letters of the second line.[1]
| E | J | P | U | Z |
| D | I | N | T | Y |
| C | H | M | S | X |
| B | G | L | R | W |
| A | F | K | Q | V |
References
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