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The British National Grid enables a recognised reference to be given to any location in England, Scotland and Wales. Map references using the National Grid can consist of 2 letters followed by 2, 4, 6, 8 or more numbers, or can be given using numbers only. The more numbers used, the more precise the map reference is.

The letters refer to the 100km grid square the reference is within.

The first half of the numbers following the letter refer to the east/west position (called an easting), while the second set refers to the north/south position (called a northing).

As the following grid squares: HP, HT, HU, HW, HX, HY and HZ are more than one thousand kilometres north of the grid's origin the numeric value of the square's second letter is represented by two digits. When creating numeric grid references for these squares the northing increases by one digit so HZ1234 becomes 412, 1034 and HP567123 becomes 456700, 1212300.

An example map reference ST391578 consists of 2 letters (ST) that identify the 100km grid square, 391 is the easting, and 578 is the northing. This map reference is precise to the nearest 100 metres.

The 100km grid square ST is shown below.

Each 100km square is then broken into 100 10km squares and referenced by the easting first, then the northing. The two squares on the diagram shown below would be referenced as ST64 and ST87 respectively.

So the 10km square for our grid reference ST391578 is referenced as ST35:

And the 1km square is referenced as ST3957:

Our grid reference ST391578 can be used to locate Yarberry Standing Stones.

Alternatively you can used the full numeric grid reference by substituting 3 and 1 for ST as shown in the following table.

Map references are normally displayed in the status bar at the bottom of the map window when the cursor is hovering over a point on the map:

They are also displayed after clicking the 'Where am I?' tool then clicking on the map on the point you want the grid reference for:

While MAGIC does not store IACS data, IACS compliant field numbers can now be viewed using the Where am I? tool in the interactive map – see the help library for details of how this tool works. Go to the IACS Compliant Field Numbers page for further information on how IACS field numbers are formed.