For the purpose of this tuitional we will concentrate on the Landranger style map of which there are 204 in total.

Each map covers an area of 40 x 40 Kms (25 x 25 mls)

A series of vertical and horizontal numbered lines can be found on these maps. Called grid lines they form part of the National Grid which is based on an imaginary line to the West of Lands End. Further to this, each 100 x 100Km area has a two letter prefix, which enables a uniqueness when plotting a map reference.

The examples below show how to calculate first a six then an eight figure map reference.

Let us use The Basic Roamer^{ }5 to plot the six figure map reference: **093 447**

So, with LR 147 map open and laid flat, find the vertical grid line (Easting 09) and the parallel grid line (Northing 44) Place The Basic Roamer onto the map, with the top Right hand corner at the point of the grid square where the vertical line (09) joins the horizontal line **44**

Now move The Basic Roamer along, towards the right (Eastwards = Easting) to a point which is 3 tenths of the grid square from gridline

Maintain this part of the plot, by holding The Basic Roamer flat against the map, now slide it towards the top of the map (Northwards = Northing) to a point which is 7

The second example allows us to utilize the The Basic Roamer^{ }to plot an eight figure map reference: **7435 7695**

For the purpose of this excercise we are utilizing Ordnance Survey Landranger map number **147**Again, open your map to expose the top left hand area in this case, find the vertical grid line

Now move The Basic Roamer along, towards the right (Eastwards = Easting) to a point which is 31

Maintain this part of the plot, by holding The Basic Roamer flat against the map, now slide it towards the top of the map (Northwards = Northing) to a point which is 91

As can be seen, this reference highlights precisely the famous Devils Bridge waterfall found next to the A4120/B4574 road junction in the Welsh countryside.