Grid References: Pinpointing Locations Precisely

📐 Grid References: Pinpointing Locations Precisely

Figure 1: Grid References — 4-figure (1 km square) and 6-figure (100 m precision)

OS maps are divided into a grid of numbered squares. The vertical lines are called eastings (they increase going east, left to right). The horizontal lines are called northings (they increase going north, bottom to top). Every location on the map can be described using these grid lines.

The golden rule — and the most important phrase in map skills — is: "Along the corridor, then up the stairs." Always read the easting (horizontal position, along the bottom) before the northing (vertical position, up the side). Get this order wrong and you give a completely different location.

4-Figure Grid References

A 4-figure grid reference identifies a 1 km × 1 km square. It is not a point — it is an area. The reference is formed by taking the easting of the left-hand (western) edge of the square, then the northing of the bottom (southern) edge.

6-Figure Grid References

A 6-figure grid reference pinpoints a location to a 100 m × 100 m square — ten times more precise than a 4-figure reference. To achieve this, each 1 km grid square is mentally divided into tenths (10 equal strips in each direction).

Checking yourself: Your 6-figure reference should start with the same two digits as the easting from your 4-figure reference, and the 4th and 5th digits should start the same as the northing from your 4-figure reference. If your 4-figure was 4210 and your 6-figure starts 37..., something has gone wrong.