Reading and Giving Grid References or OS Coordinates
A grid reference allows you to reference any 100m x 100m square in mainland Britain (England, Scotland & Wales).
A complete grid reference comprises two grid letters (which define a particular 100km x 100km square) plus a 6 figure number (which defines a particular 100m x 100m square within that larger square). For more information on grid letters - see The National Grid.
1. Find the blue vertical grid line immediately to the west (left) of Point 'A' - the '78' grid line. This grid line represents the first two numbers of the grid reference - 78. (Called 'The Easting' - because it increases as you travel East)
2. Next, find the horizontal grid line immediately to the south (below) of Point 'A' - the '44' line. This represents the fourth and fifth number in the grid reference - 44. (Called 'The Northing' - because it increases as you travel North)
3. Imagine this 1km square is divided into 100 smaller squares - 10 along the bottom and 10 up the side - represented as grey lines in the illustration above.
4. Estimate how many smaller squares point A is east (right) of grid line 78. This represents the third number of the grid reference - 5.
5. Similarly, estimate how many smaller squares point A is north (above) of grid line 44. This represents the sixth number of the grid reference - 2.
6. Finally, add the two grid letters which define the relevant square to the front of the reference - SD. These letters will be found in the map margin. You now have a complete grid reference for a 100m x 100m square.
Remember: Grid References are always read Eastings first followed by the Northings. This can be easily recalled using the phrase:
Go Along The Corridor (Eastings) before going Up The Stairs (Northings)
Note: It is important to note that the complete grid reference defines an area of 100m x 100m NOT a particular spot.