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Explanation of the Irish National Grid

The Irish National Grid is a map reference system covering Ireland (ie Northern Ireland and Republic of Ireland).The X/Y (East/North) axis 0/0 point is south west of Ireland. Single character alphabetic codes identify 100 Km squares, these subdivide into 10 Km squares numbered 0 to 9 West to East and South to North from the left corner. Eastings are quoted before Northings.

Irish 100 Km National Grid squares

500	A	B	C	D
400	F	G	H	J
300	L	M	N	O
200	Q	R	S	T
100	V	W	X	Y
0	100	200	300	400

The underlying principles of the UK and Irish Grids are identical, ie alpha referenced prime 100 Km squares which subdivide into a hundred 10 Km squares etc. The UK system uses two alpha characters because of the number of 100 Km squares required. The Irish system requires in total 20 prime squares, hence they need only a single alpha character.

The two systems have different points of origin ie 0/0 point (X/Y axis intersection point). An approximate conversion of Irish Grid References to those of the UK National Grid is achieved by adding 160 Km to Irish Km Northings and subtracting 182 Km from Irish Km Eastings.