Knowing grid references is an important map reading skill which could save your life!
Grid references are a series of letters and numbers which give location on a map. They are written with the sideways number (Eastings) first followed by the vertical number (Northings). This is often remembered with the expression 'along the corridor then up the stairs'.
At Walk Snowdonia, we've created this comprehensive guide to Grid References. For more information about other important map reading skills, take a look at our guide all about the map reading basics you should know.
What is the purpose of a grid system on a map?
The Grid System uses a numerical system for defining a specific location identifying where on a map a feature or person is. This is particularly useful in mountain rescue incidents or to relocate if you are lost.
What is the grid system?
The grid system is a series of grid lines. These are vertical lines and horizontal lines which are drawn on a map creating squares. These squares are assigned a number (or letter).
How the Grid System works
The UK is divided into 500km Squares of the National Grid which are assigned a letter. These squares are subdivided into smaller 100km squares that cover Great Britain and these are assigned another letter. Wales is covered by the Grid Square 'S'. North West Wales and Snowdonia North is covered by the Grid Square 'SH'.
These 100 km squares are subdivided again into 1km squares and this time assigned numbers. These squares are the ones which are drawn on most topographical maps which are used for navigation. The 1km squares are blue on OS maps and grey on Harvey maps. These numbers are the ones used in a four figure grid reference.
What are Grid References?
Grid references are a series of numbers (and letters) which use the Grid System to locate something on a map.
The letters identify a square in Great Britain and the numbers provide the location within that square giving a unique location.
A four figure grid reference is the location of a 1km square. These are the squares drawn on most topographical maps.
A six figure grid reference gives the location of a 100m square. This is a small enough area to work with most of the time in the mountains.
An eight figure grid reference is the location of a 10m square. This gives an exact location for most things on a map. There isn't usually anything smaller than 10m drawn on a topographical map that is used for hiking.
A ten figure grid references gives the location of a 1 x 1m square. This is an extremely precise location and this level of precision isn't usually necessary in the mountains.
How do you read grid references?
Grid references are read by giving the sideways number (Eastings) first, followed by the vertical number (Northings). This is often remembered with the expression 'along the corridor then up the stairs'. You might also hear 'you crawl before you walk'.
How to read four figure grid references
To read or provide a four figure grid reference you simply start in the bottom left and read the numbers which are printed on the map starting with the sideways number (Easting), followed by the vertical number (Northing). 'Along the corridor then up the stairs'.
To ensure there is no confusion about which part of the National Grid you are referring to the numbers are sometimes preceded by the letters for the 100km squares 'SH 27 94'.
How to read six figure grid references
For a six figure grid reference divide the 1 km square which is drawn on the map into tenths. This is not drawn on a map but on the graphic below it is shown by the grey dashed lines. This is measured accurately on a map using the Roma Scale on the side of the compass.
The purple circle is two tenths of the way across the grid square and six tenths up so the complete grid reference is '602 486'.
This is the level of detail often used in the mountains.
How to read eight and ten figure grid references
For an eight figure grid reference divide the grey dashed squares into tenths again. This gives a square of 10m x 10m. This is usually the smallest object or feature that is shown on a map.
For a ten figure grid reference divide this 10m square into tenths again.
Common mistakes when reading grid references
The easiest and most common mistake is to give the numbers in the wrong order. Remember 'along the corridor then up the stairs'.
It is important to match the Roma Scale on the compass with the scale of map being used. A common error is to measure with the wrong one.
Sometimes people confuse the faint blue grid lines with streams on OS maps as they are the same colour. The faint blue lines of the grid are perfectly straight, whereas streams are wiggly.
A really easy mistake to make is to read the Roma Scale or grid number from the top left of the map. This is how you normally read. Remember to start in the bottom left and go 'up the stairs' and not down the stairs. Therefore start in the bottom left and go from bottom to top (aka. up).
This means Snowdon/ Yr Wyddfa summit is in the 54 square and not the 55 square. Also notice that for a 6 figure grid reference it might look like the compass is 'upside down', but the Roma numbers start on the 54 line so 549 is nine tenths of the way up the 54 square.
Get skilled up in map reading with Walk Snowdonia
Giving people the skills to go on their own adventures is our passion. On our Beginners Map Reading Course you will learn and practice all of the skills you need to feel confident navigating around the mountains. All of our map reading courses take place in the spectacular surroundings of the Snowdonia National Park.
We also offer Bespoke Navigation Courses for people wanting to focus on specific skills such as doing lots of grid references or compass bearings. What are you waiting for? Contact us today for a fun adventure!
Is latitude and longitude the same?
Latitude and longitude is a different and more precise system than grid references. It us used by satellites and GPS. The latitude and longitude of Snowdon summit is 53.068574, -4.076233
Grid references are a really useful navigation tool and in a rescue situation could save your life. Learn them, practice using them and enjoy the mountains!
Want to test your new map reading skills at Snowdonia National Park? Learn more about the area and plan your trip using our blogs: