Grid Lines Explained
Ordnance Survey maps are covered in a series of faint blue lines that make
up a grid. The lines have numbers accompanying them that allow you to
accurately pinpoint your location on a map. Once you have located where you
are, the grid system makes it simple to give others (such as mountain rescue)
an accurate description of your location. This description, which will be a series
of numbers, is known as a grid reference.
Before you begin to look at grid
references it is important to be aware
that all the numbers going across the
face of the map, for example, left to
right, are called eastings (this is because
they are heading eastward), and similarly,
all the numbers going up the face of
the map from bottom to top are called
northings (again because they are
heading in a northward direction).
There are two main types of grid reference:
• 4-figure – for example, 1945, this indicates a single kilometre square on
an Ordnance Survey map.
• 6-figure – for example, 192454, shows a point within a square.
4-figure map references
When giving a 4-figure grid reference you
should always give the eastings number
first and the northings number second,
very much like when giving the reading
of a graph in school – you must go along
the corridor/hallway (horizontal) and then
up the stairs (vertical).
For example, the number 2 in the
diagram opposite is 19 across and 45 up
and therefore the 4- igure grid reference
The numbered squares on the diagram above would have the following
4-figure grid references:
6-figure map references
Square 1 = 18 45
Square 2 = 19 45
Square 3 = 18 44
Square 4 = 19 44
|Having worked out the basic 4-figure grid reference,
for example, square 3, 18 44 in diagram 2,
imagine this square is further divided up into tenths.
Using the example opposite, the grey box is in the square 1844.
More accurately it is 7 tenths across and 8 tenths up within the grid square 1844 and therefore has the 6-figure map reference 187448.
The shapes on the map opposite would have the following 6-figure grid references:
Grey square = 187448
Red dot = 185443
National Grid lines
As well as numbered grid lines, Ordnance Survey maps have
codes made of two letters. These
two letter codes can be found
printed in faint blue capitals on
Ordnance Survey maps. The
whole of Great Britain is divided
into squares of 100 km and each
square is given two letters.
will be a diagram within your
map’s key showing you which
areas of your map fall into different
squares of the National Grid.
When you quote your six-digit
grid reference you should put the
two letters of the area you are in
before the numbers. This means
that there is no doubt or confusion
about your location. For example,
you may be at grid reference
509 582 in south-west Scotland.
The complete grid reference you
should quote would be
NX 509 582 (without the letters the
numeric reference would be repeated in every 100 km square).