Map reading skills: How to use a compass

Updated March 2020.

SBNav2Week five in our six-week blog series on map reading skills focuses on the compass. Map reading is an essential skill for any explorer or outdoor enthusiast. We’ve teamed up with Steve Backshall to record a series of videos to remind you of the basics and help you feel confident with your map.

So far we’ve covered which OS map you needunderstanding map symbols and making sense of contour lines and how to read a grid reference. Today we’re covering the compass. Next week, our final blog in the series will cover:

  • Understanding magnetic north

Each week we’ll share Steve’s video with you, give a summary in the blog and point you in the right direction of further resources and details. Hear what Steve has to say about knowing your compass and how to take a compass bearing in these two short videos:

Why do I need a compass?

Learning how to use a compass is an important outdoor skill; not just for walkers, but cyclists and runners too. It’s good to take a compass with you, but even better if you know what to do with it! A compass helps you to find where you are and find your way; this is very useful but can be critical if you get lost and visibility is poor.

Compass features

Compasses come in many designs, but most compass features are the same as those found in an all-time classic compass like the Silva Ranger. You need to make use of some or all of the compass features for different tasks. Before you can use a compass to navigate you need to be familiar with the main features.


1. Base plate – this is what the compass is mounted on and has rulers and scales on it to help you measure distance. You will also notice a black line running the length. When taking your bearing on the map – this line can be used to line up where you are and where you want to go to.

2. Compass housing – within the rotating bezel there is the magnetic needle (see number 3 for details). Around the bezel are marked 360° of a circle – these will give you your bearing.

3. Compass needle – it is floating in a liquid (usually alcohol) so it can freely rotate. The red end always points to magnetic north.

4. Orienting lines – they are fixed within the compass housing and can be aligned with the easting lines on your map to ensure you accurately align the compass with grid north.

5. Orienting arrow – this is fixed within the compass housing. When you come to take your bearing – you will align the compass needle with this arrow.

6. Index line – on some compasses, as shown here, it is a fixed black line within the bezel, on others it could be an arrow on the base plate. It is at this mark that you take your compass bearing.

7. Direction of travel arrow – this does what it says on the box – this is the direction in which you will be traveling in after taking your bearing.

8. Compass scales or romer scales – these can help you measure distance and accurately help you work out your six-figure grid reference.

The main working part of a compass is the magnetic ‘needle’ that floats on a central pivot. The red end always points to the Earth’s magnetic north pole and the outer ring is marked with the cardinal points of the compass (N-S-E-W) and every 2 degrees. These markings are used to get bearings (the direction from where you are, to where you want to go).

If you rotate the ring to line-up the red north of the needle to the red arrow on the baseplate, a bearing can be taken from the compass ring.

Know your norths

Before we move on to how to use a compass we also need to understand the three different norths that there are. Have a look at the legend on your Ordnance Survey map and you will see that there is a section called North Points. When it comes to compass navigation – this is an important section of the legend.

There are three norths. The first is true north – this is where the north pole is and for the purposes of navigation can be ignored. The next one is grid north – this is the top of your map. It’s the same for all Ordnance Survey maps which means that rather than being one single point – it is a line, as if the world is flat and all along the top is north. The third and final north is magnetic north. This is where the compass needle points to and is governed by the magnetic field of the earth. We’ll be talking about this in more detail next week.

How to take a compass bearing

To start with you need to know where you are on the map (point A) and where you want to go to (point B).

Line up point A and B with either the side of your compass or one of the black lines running down the base plate, making sure that the direction of travel arrow is point in the direction you want to go in (so towards point B).

Now you want to turn the compass housing bezel so that the “N” on the bezel and the orienteering arrow are point to grid north (the top of the map). To help do this – make sure that the orienteering lines are lined up with the easting lines on the map.

Now you can lift the compass off the map.

Look at the index line – this has given you your bearing from the map. We now need to add the 2° to this to make grid north match magnetic north.

Stand up with the direction of travel arrow pointing directly in front of you. Walk around in a circle until you have the compass needle lined up with the orienting arrow.

Look up, following the direction of travel arrow and pick a natural feature or landmark that is directly in line with where you are looking / where the direction of travel arrow points to.

Walk towards this landmark and once there check your bearing, pick another landmark to walk towards. Repeat this until you reach your destination (point B).

If you’re unsure about using a compass the best thing to do is get the map of an area you know really well, perhaps somewhere local to where you live, and is somewhere that you wouldn’t usually need a map to get around. Take yourself off for a walk, using the map and a compass to navigate your way. This way you shouldn’t get yourself lost (as it’s an area you know really well) and you can check that the direction you think you should be traveling in matches what the compass is telling you!

Top tips for beginners

Make sure that the direction of travel arrow is pointing in the direction you want to walk in – it’s called the direction of travel arrow for a reason!

Always make sure that the orienting arrow is pointing to grid north (the top of the map) rather than grid south (the bottom of the map) – even if you are walking south – the orienting arrow still needs to point north.

Unless you always want to walk due north – follow the direction of travel arrow rather than the compass needle.

Make sure that the landmark you pick is a feature on the landscape that is not liable to move – pick a tree, gate post, gorse bush or boulder for example rather than a cow, sheep, person or bird!

You can download resources from our Map Zone (aimed at children) that take you through how to to use a compass with more examples and a look ahead to magnetic north.

Happy exploring! I’ll be back next week to talk about magnetic north.

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27 Responses

  1. Justin Case

    OK total newbie to all this …i live in Caernarfon so when i take a bearing off the map do i then add 2 degrees to the reading to adjust for the magnetic diffrence…eg….if the map bearing said 65 degrees would i need to add 2 degrees to make it 67 degrees to be on the right track….(im assuming 2 degrees is the diffrence for this date 31-12-2015 but to be honest im not sure of this ) please help as i just dont get it

    1. Hi Justin

      The degree of magnetic variation is different across Britain, so we always show the variation for each area on each OS map. This is shown on the map legend or key inside each of our paper maps, along with the date it was calculated. If you’re a complete beginner, you could try working through our booklet on map reading skills here: https://www.ordnancesurvey.co.uk/docs/ebooks/map-reading.pdf

      There are also many organisations across Britain who offer map reading and navigation courses to ensure people can safely get out and explore the country.

      Many thanks

    2. Ian

      The easiest way to remember the mag variation (declination) rule is GRID (from the Map) to MAG, ADD. MAG to GRID, Get Rid.

      So, if you take a bearing from the the map you need to ADD the variation and if you take a bearing from the compass to attribute it to the map you need to take it off.

      Easy peasy, lemon squeezy.

      1. Sarah

        The old mnemonic “Grid to Mag, Add. Mag to Grid, Get Rid.” only works when magnetic north is west of grid north so I’m afraid it doesn’t work in the far south west anymore!

        N.B. Magnetic variation and declination aren’t synonymous in the UK. Magnetic variation is the difference between grid north and magnetic north whereas declination is the difference between true north and magnetic north. On UK maps, grid north doesn’t equal true north, so we’re adjusting our compass bearings for magnetic variation not declination. (In countries where grid north equals true north the magnetic variation and declination are identical and the two words can be used interchangeably.)

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  3. Deborah

    This is fabulously easy to follow! Really enjoyed the short snappy videos break this down into easy chunks of information and mean it is easier to absorb. Thank you for taking the time to do this.
    Thank you from a Ten Tors prospective parent!

  4. Brian Spencer

    Hi Gemma.
    I have a Silva type 4/45 plate compass. On the inside of the rotating bezzle there is the compass needle and a scale from 0-360 deg which I understand. On the raised outside edge of the bezzle is a scale which starts at N then goes 02, 04, 06 etc reaching 10 at 60 deg West before ascending in divisions of 2 until 62 when it reaches N again. This bezzle rotates with the inner 0-360 deg.

    I can not work out what this scale does, nor unfortunately can the staff in my local outdoor shop. Can you help please? Thank you, Brian

    1. Hi Brian

      I’ve had a chat with my Customer Service team colleagues on this. They’ve had a quick internet search and believe the compass in question is a military style compass of some description. The figures on the raised part of the Bezzle are known as “Mils”.

      We have found an internet forum that you may wish to look at to find out a little more information about. This can be accessed here: http://micronavigation.com/forum/index.php?topic=38.0

      Otherwise, if you’d like to email customerservices@os.uk and include a photo of the device they can try to investigate further.

      Many thanks

    2. Ian

      The scale on the raised bezzle is mils, short for mils radians. Mils are used by the military and the scale is divided to 6400 mils for a circle (64, on the bezzle) which is 360 degrees on a normal compass bezzle. When used by a competent user, mils can be more accurate when taking/giving a bearing. In the military mils can also be used for judging scale and distance.

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  7. Simon Beagley

    I know how to use a compass but I can’t work out how to attach the neck cord with the fittings supplied with my new OS compass

  8. Craig day


    As an ex squaddie I use a silva compass but in mils, I was always taught that the magnetic variation is annual and so if the map is 10 years old then the variation needs to be multiplied by 10 then added to the bearing, is this still the case?

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  10. Mick Dunn

    Nice one, needed to revise myself on the basics as its been around 11 years since i used a map and compass and planning a trip up Ben Nevis later this month. This has been a great help.

    Thank you


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  12. Neil Allso

    I think it would be good for clubs and enthusiasts etc to learn triangulation to find out where they are from 3 landmarks. This has got me out of trouble many times in the past when I was in the military

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