National grid

The national grid is a system of grid references used by the Ordnance Survey in their maps of the Great Britain. First, the area is divided into a number of squares, 10km by 10km.

HL	HM	HN	HO	HP	JL	JM
HQ	HR	HS	HT	HU	JQ	JR
HV	HW	HX	HY	HZ	JV	JW
NA	NB	NC	ND	NE	OA	OB
NF	NG	NH	NJ	NK	OF	OG
NL	NM	NN	NO	NP	OL	OM
NQ	NR	NS	NT	NU	OQ	OR
NV	NW	NX	NY	NZ	OV	OW
SA	SB	SC	SD	SE	TA	TB
SF	SG	SH	SJ	SK	TF	TG
SL	SM	SN	SO	SP	TL	TM
SQ	SR	SS	ST	SU	TQ	TR
SV	SW	SX	SY	SZ	TV	TW

Within each square, eastings and northings are given as a code. For example, HL35 means 'square HL, 3 km east, 5 km north'. Additional precision is specified by longer numbers - SS390465 means 'square SS, 3900 metres east, 4650 meters north'.