Map reading explained

Improve your map reading skills with the help of these expert tips from our friends over at OS Maps. From map symbols, to contour lines and coordinates, here’s the basics explained…

If you like scaling mountains or heading out into the hills hiking, then you’ve probably looked at a map or two, but do you know how to read one? When venturing further afield it’s a good idea to know where you are going to keep safe and make your walk an enjoyable one.

Navigation apps like OS Maps will enable you to follow a route and know your location, but we always recommended taking a paper map and compass too, especially if you’re going off the beaten track. A basic level of map reading knowledge will help you on your way, allowing you to understand the mapping on your device and make use of your paper backup. So, let’s start with the basics.

Map Symbols

Map Symbols

Knowing what each symbol means on a map will give you a point of reference to help you determine where you are and where you want to go. What’s more, they allow you to see points of interest like pubs and car parks, plus public rights of way. Map symbols can vary across different brands of maps, so let’s take one of the most common for walking and learn about the map symbols on an OS Explorer Map.

Contour lines and relief

Hills, slopes and mountains are represented on a map using contour lines. By studying these lines, you can work out lots about the surrounding terrain including gradients of hills, valleys and the steepness of climbs.

Contour Lines

A contour is a line drawn on a map that joins points of equal height above sea level - on 1:25 000 scale maps (OS Explorer) these lines are brown and each line will have a number indicating the height. Some maps may not show the height on every line, so if you can’t see a number, follow the line until you can, or look at the line below/above. On maps with a 1:25 000 scale, the interval between contours is usually ten metres, although in parts of the country that are flatter it may be five metres. Contour numbering reads up hill – in other words the top of the number is uphill and the bottom is downhill.

You can find out how steep a slope is by looking at the spacing between each contour line. The closer they are together, the steeper the slope. This is particularly useful when planning a route as you may want to avoid slopes that are so steep, they are impassable.

Find out more in this beginner’s guide to contours and this advanced guide.

Using a compass

How to read a compass

Before you learn to use a compass, familiarise yourself with the terminology used for each part.

1. Baseplate - The mounting of the compass. Clear, so when placed on top of the map you can still see the map features.

2. Compass housing - Contains the magnetic needle and has the points of the compass printed on a circular, rotating bezel.

3. Compass needle - Floats in liquid so it can rotate freely but without being too sensitive to movement, the red end points to magnetic north.

4. Orienting lines - Fixed within the compass housing and designed to be aligned with the eastings on a map.

5. Orienting arrow - Fixed within the compass housing, aligned to north on the housing. Enables conversion between grid and magnetic north.

6. Magnetic variation – technically not part of the compass but allows accurate adjustment for magnetic variation or declination

7. Index line - Fixed beneath the rotating bezel of the compass, it marks the bearing you wish to travel along.

8. Direction of travel arrow - Shows the direction that you want to travel along once you have taken your bearing. It is an extension of the index line.

9. Compass scale - Displayed along the edge of the base plate so you can measure distances on maps.


Here are five steps on how to use a compass. Remember, the red end of the compass points to north, the black end points to south. For a more in depth guide, check out this guide to using a compass and find out more about which compass you may need.

1. From your starting point on the map, place the index line on an imaginary line between where you are now and where you want to be – with the direction of travel arrow on the base plate pointing the way. Start by drawing a line from A to B now.

2. Holding the baseplate in place, rotate the compass housing so the orienting arrow lines up with grid north on the map. The orienting lines should be parallel with the vertical blue grid lines (eastings)

3. Your compass does not point to grid north. Magnetic north throughout Great Britain can range from 0º to 5º. The amount of variation changes every year, so check your OS map to work out the most current value. You’ll find this in the map legend. Add magnetic variation to your bearing by rotating the compass housing.

4. Take your compass off the map. Hold your compass flat at waist height and turn yourself until the red needle meets up with the letter N and is positioned over the orienting arrow. You’re ready to go. The red direction of travel arrow will point the way.

5. Compass readings are also affected by the presence of iron and steel objects, so be sure to look out for – and stay away from – pocketknives, belt buckles, mobiles and GPS devices when using your compass.

OS Map reading

As an alternative to using a compass to orientate your map, you can use your eyesight. This method will only work if you are in an area with visible prominent features or landmarks and know how they are represented on a map.  First, locate yourself next to a feature or landmark and place your finger on the map at the point where you are standing. Then begin to rotate the map so that other features and landmarks on the map begin to line up with the actual ones you can see. The map is now orientated with the land, although not as accurately as it would be using a compass.

Grid references and coordinate

Both grid references and coordinates help identify a location and are often used when navigating or letting someone (like Mountain Rescue) know where you are. Although the two terms are often used interchangeably, coordinates are different to grid references. Coordinates give you a precise exact position anywhere in the world, where as grid references will determine which grid square, you’re located in – in Britain. Although coordinates are more precise, you cannot find them on a paper map. You can, however, find your location using grid references on an OS map – here’s how..

How to read a map

In Britain, every map has a series of horizonal and vertical grid lines to break it up into grid squares. The simplest way to determine a location’s grid reference is to look at the grid lines on a map and put the two together, reading the horizontal line left to right (called eastings) first, followed by the vertical lines from bottom to top (called northings). These are linked to the National Grid which provides a unique reference system and can be applied to all OS maps of Great Britain, at all scales.

There are four-figure grid references (identifying a single kilometre square) and six-figure grid references (identifying a 100-metre square within a single kilometre square) for every place in Britain. The larger the grid reference, the smaller and more precise the area is. As well as numbered grid lines, OS maps have a two-letter prefix. The two-letter prefixes can be found printed in faint blue capitals on OS maps. The whole of Great Britain is divided into squares of 100km and each square is given two letters. These letters should be put before the four or six-figure grid reference to ensure there is no confusion to your location. Find out more in this beginner’s guide to grid references.

You may have heard of longitude and latitude when talking about coordinates. All the longitude lines are equal in length and run from one pole to the other and all latitudes are parallel, creating a grid. However, this grid is different to the British National Grid, as these lines represent the angle of the point with respect to the world’s core, as opposed to a 2D map.

Digital map reading for OS Maps

GPS devices use the decimal degree system to give a reading of the longitude and latitude (coordinates), so knowing how to look at (and not necessarily determine) your coordinates is important. With any map, it is important to check which grid system it is using, especially if combined with a GPS device or travelling abroad. Find out how you can pinpoint your location on a map.

Feeling inspired?

An OS map can help you discover new places and make sure you safely find your way. It can be vital when exploring the outdoors, if you know how to read it that is. Now you understand the basics, expand your knowledge with these advanced map reading guides.