Tetrad (unit of area)
Encyclopedia
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
.
Tetrads are sometimes used by biologists for reporting the distribution of species to maintain a degree of confidentiality about their data, though the system is not in universal use.
The tetrads are labelled from A to Z (omitting O) according the "DINTY" system as shown in the grid below, which takes its name from the letters of the second line.
Ordnance Survey
Ordnance Survey , an executive agency and non-ministerial government department of the Government of the United Kingdom, is the national mapping agency for Great Britain, producing maps of Great Britain , and one of the world's largest producers of maps.The name reflects its creation together with...
national grid
British national grid reference system
The Ordnance Survey National Grid reference system is a system of geographic grid references used in Great Britain, different from using latitude and longitude....
, and then refers to any of the 25 such squares which make up a standard hectad
Hectad (unit of area)
A hectad is an area 10 km x 10 km square.The term has a particular use in connection with the British Ordnance Survey national grid, and then refers to any of the 100 such squares which make up a standard 100 km x 100 km myriad; these are denoted using the letter code of the...
.
Tetrads are sometimes used by biologists for reporting the distribution of species to maintain a degree of confidentiality about their data, though the system is not in universal use.
The tetrads are labelled from A to Z (omitting O) according the "DINTY" system as shown in the grid below, which takes its name from the letters of the second line.
| 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 |