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 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

1. ^ ^{a b c} "DINTY Tetrads". Kent and Medway Biological Records Centre. http://www.kmbrc.org.uk/recording/help/gridrefhelp.php?page=6. Retrieved 23 December 2008. 
2. ^ "National Grid References". Sussex Biodiversity Record Centre. 2008. http://www.sxbrc.org.uk/biodiversity/recording/ngr.php. Retrieved 23 December 2008. 

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