Sheffield Breeding Atlas 2003

Sheffield Breeding Bird Atlas Project 2003

Choosing Tetrads

Once you have decided you would like help with the collection of data for the new Sheffield Breeding Bird Atlas you will need to choose one or more tetrads to cover. After following the instructions below it is important that you email David Wood to confirm your choice of tetrad[s] and for David to confirm that it/they is/are still available.

If you are not familiar with the tetrad system you can follow the instructions below to work out the tetrad designation of your preferred locality. At this stage you will need to look at the information within the "MAPS" link [above] to determine which tetrads are not yet covered.

The OS grid reference for the centre of any tetrad (all of which are preceded with SK) can be gained by applying the system below, with the letters X and Y being replaced with the numbers 1 and 7 (for the 10 km square SK17), 1 and 8 (for the 10 km square SK18), etc.

E = x10y90	J = x30y90	P = x50y90	U = x70y90	Z = x90y90
D = x10y70	I = x30y70	N = x50y70	T = x70y70	Y = x90y70
C = x10y50	H = x30y50	M = x50y50	S = x70y50	X = x90y50
B = x10y30	G = x30y30	L = x50y30	R = x70y30	W = x90y30
A = x10y10	F = x30y10	K = x50y10	Q = x70y10	V = x90y10

E.g. For tetrad "sk28s":

any "s" tetrad is "x70y50".

So with x and y as 2 and 8 (from sk28), the grid reference for "sk28s" will be "s k 2 7 0 8 5 0".

For a more detailed map of any tetrad, follow the instructions below:

Visit www.streetmap.co.uk and click on the "OS grid" option.
Insert the grid ref. skXXXYYY (see table above) and click ‘search’.
Click the minus sign below the bottom right-hand corner of the map that appears (to the right of the decreasing arrows next to where it says ‘Large Map’).
The yellow arrow points towards the central axis of the tetrad, which is made up of four 1000m [1km] squares.