National Grid References - An introduction

The position of any point in Great Britain can be described by its National Grid reference. These references are often used in conjunction with Ordnance Survey maps, and are used to give the names of individual Ordnance Survey data tiles.

Grid References are made up of:

• two letters, followed by
• an even number of digits, optionally followed by
• a quadrant name: "NW", "NE", "SW" or "SE", standing for North West, North East, South West and South East.

These components are usually written without spaces. However, spaces are included here for legibility.

Examples of Grid References are: SK 07 ; SK 07 SW ; SK 042366

Where Grid References are used to identify Land-Line tiles, then

• Urban tile names (500m * 500m) are of the form SK 0472 SE;
  i.e. 2 letters, 4 digits, quadrant name
• Rural tile names (1km * 1km) are of the form SK 0474;
  i.e. 2 letters, 4 digits
• Upland tile names (5km * 5km) are of the form SK 07 SW;
  i.e. 2 letters, 2 digits, quadrant name

The First Two Letters

Two letters together identify a 100km square, and are derived as follows:

The first letter identifies a 500km square, from the diagram shown here. The letters are allocated in alphabetical order from left to right and top to bottom, and omitting the letter "I".

Ordnance Survey's products lie completely within four of these 500km squares: H, N, S and T.

Each 500km square is then divided into twenty five 100km squares, and these squares are then labelled using the same pattern of letters. The resulting 100km squares covering Great Britain are shown here.

The digits

The digits identify a location within a 100km square. The first half of the digits give the Easting, or distance East from the edge of the 100km square. The second half of the digits give the Northing, or distance North from the edge of the 100km square.

If there are:

• 2 digits: the Easting and Northing are each in units of 10km;
• 4 digits: the Easting and Northing are each in units of 1km;
• 6 digits: the Easting and Northing are each in units of 100m;
• 8 digits: the Easting and Northing are each in units of 10m;
• 10 digits: the Easting and Northing are each in units of 1m.

The quadrant name

If there is a quadrant name present, it indicates one quarter of the area indicated by the rest of the Grid Reference.

For example, within the square SK: