Grid Reference - It is usually an eight character item of the form SK123456 where SK is the position in the picture on the right and the 123456 defines a location within that square to within 100 metres.

Any in depth description of co-ordinate systems is given in the OS document.

To explain.

The country is divided into a set of 100Km squares, each square is given a two character reference. Each square can be divided up into 100 1 Km squares. So define one of these squares one needs two numbers between 0 and 99. For instance SK 12 34 defines one such square, usually written without the blanks SK1234.

To give a unique reference defining the position of a point to within 100 metres requires a two digit area number and a six digit reference (two numbers between 0 and 999).

For instance if you look at an Ordnance Survey map of the Peak District the area code for most of the map is SK. The reference of

• Matlock railway station would be 295602, the full reference being SK295602
• Winster would be 240605, the full reference being SK240605

See the legend on your maps for a description of how to define Grid References or the link below.

https://www.ordnancesurvey.co.uk/resources/maps-and-geographic-resources/the-national-grid.html