Magnetic north is on the move again

One thing that many people don’t realise when they’re new to outdoor walking and navigation is that their compass doesn’t point to grid north – except by coincidence in some areas. The compass needle is attracted by magnetic force, which varies in different parts of the world and is constantly changing.

The magnetic variation throughout Great Britain has been a few degrees West of grid North with the amount of variation changing every year. For years the number has decreased, and now in the far South West of Britain, the North on your compass lies to the East of the North on your map for the first time since before the Ordnance Survey came into existence (in 1791 if you’re interested).  The change is slowly crossing the country, but for now can only be appreciated in our Custom Made maps with a centre to the West of Penzance.  Buy one now and you will find a new icon we have created in the legend to show the new relationship between the three Norths (magnetic, grid and true). 


We show magnetic north on all of our maps (and state the date it was calculated), but for now only Custom Made will be showing the latest figures, which we obtain from the British Geological Survey (BGS) each year.

How to use a compass:

Decide on the route of your walk and identify your starting point on the map. Place your compass on the map. Make sure the ‘direction of travel arrow’ is pointing in the direction of your route across the map. The easiest way to line the arrow is to place the side of the base plate so it crosses your starting point and the next destination of your journey.

Carefully holding the compass base plate still, you will need to turn the compass housing so the orientating lines match up with the eastings (the vertical, north–south lines) on your map. Holding the map flat and the compass still, you need to rotate your body so that the compass needle settles in line (opposite) with the index line. To fully orientate your map you will need to make some adjustments for magnetic variation.

You can properly orientate the map by carefully turning the compass housing 4º clockwise (for example, depending on where you are in Great Britain and by checking on your map legend) and then turning your body again to realign the magnetic needle with the index line. Your map is now oriented to the north.

Find out more about map reading skills with our Map reading made easy leaflet.

46 Responses

  1. Pingback : Singletrack Magazine | Magnetic North on the move

  2. Paul Etherington

    So just to confirm, from this moment on, should we be using 4 degrees as the mag to grid variance? When teaching map and compass in the North of England

    1. Alastair Stuart

      If I understand correctly, this WMM gives a figure relative to True North, which must in turn be readjusted for Grid North for the particular area of your map.

  3. John

    Why is the difference most noted in the south west? Surely the nearer the observer is to the north magnetic pole the difference from the grid north point will be greater? Or do I misunderstand grid north and there is no “point”?


    1. Gemma

      Hi John

      The change to magnetic north gradually sweeps across the globe as the magnetic north pole is constantly moving. The change has reached Cornwall first and magnetic north is currently moving around 30km per 6 months, so the landmark moment (in our era) of magnetic north being east of grid north will eventually affect the whole of Great Britain. There’s lots of information on magnetic north out there, this explanation may help: http://science.howstuffworks.com/environmental/earth/geophysics/question782.htm

      Thanks, Gemma

  4. Pingback : Magnetic north is on the move again | Griffin ESU

  5. Pingback : Interesting Little Article | The Life & Times Of The Funky Chilli...

  6. Shamus

    Can you throw up a couple of examples…

    What would be the variation (today) on St Mary’s Isles of Scilly and , for example, Exeter?

  7. Shamus

    Thanks Gemma,

    That works a treat. I wanted to get a visual reference on the magnitude of variation for today.

    St Marys on the Isles of Scilly seems to be around 11’East and Princetown in the middle of Dartmoor is 55′ West.

    Ta very much

  8. Edward

    If you go Orienteering, you won’t need to worry about it, as all maps are already orientated to Mag North. British Orienteering, Scottish Orienteering, Welsh Orienteering & NI Orienteering have some brilliant coaches in every county. You’ll also get fit and enjoy the countryside!!

    1. Gemma

      Hi Jon

      Unfortunately, yes, as the change sweeps across the country, it seems that will be the case. It’s currently affecting west of Penzance, but magnetic north is moving around 30km per 6 months, so should be whole of GB in the next decade or so.

      Thanks, Gemma

      1. Very good blog you have here but I was curious if you knew of any user discussion forums that
        cover the same topics talked about in this article?

        I’d really love to be a part of community where I can get comments from other knowledgeable people that share the same interest.
        If you have any recommendations, please let me know.
        Many thanks!

  9. An interesting story, but the title could mislead those who do not know the background because, as you know , Magnetic North is always slowly moving – it has not suddenly shifted.

  10. Pingback : North by Northeast: The Trouble with the Earth's Shifting Magnetic Field - NaturPhilosophie

  11. Susan Macmillan

    Thanks Gemma for directing people to the grid magnetic angle calculator on the BGS website, which I look after.

    Compass needles align themselves with the local magnetic field. It is therefore a little confusing to relate the current changes in the grid magnetic angle in Great Britain to the movement of the north magnetic pole in the Arctic. The Earth’s magnetic field is more complex than that of a dipole.

    For more details please have a look at http://britgeopeople.blogspot.co.uk/2014/01/somethings-happening-to-magnetic-north.html

  12. Allen Norris

    It would be really useful if when selecting a map using Getamap the magnetic variation could be calculated and then printed out on the map.

    1. Hi Peter

      We’re really involved in mapping the features of the landscape, but would imagine that this would have an impact on those navigating at sea or in the air off the west coast as the magnetic variation currently affects those areas.

      Many thanks

  13. Gerry

    Gemma – Is Magnetic Variation cyclical ? If it is what period? I have a feeling you’re going to say it’s not quite that simple !

    1. Rob

      The British Geological Survey are the experts in this field. BGS have this useful page -http://www.geomag.bgs.ac.uk/education/earthmag.html#_Toc2075557

    1. Gringo

      James, because grid lines are straight and parallel, whereas the lines of latitude and longitude that make up the graticule are curved. Grid North and True North are aligned on the 2°W meridian for OS maps, but diverge as you come away from that line.

  14. Pingback : Navigation Skills 7 The Anatomy of the Compass - Mud and Routes

  15. Mark Roberts

    Come home GPS all is forgiven.

    Having been away from os maps and using a compass for many years i return to find the magnetic north has gone over to the east!!
    I’m no mathmatician and frankly find it all a bit confusing.
    In my army days it was add for mag and rid for grid. Am i right in assuming that this is now reversed for the new magnetic north?
    If i were to be taking bearings with a compass, in say, Snowdonia, next week, would i still need to add the relevant variation or subtract it?
    Any help would be greatly appreciated.

    1. Hi Mark

      The changes to magnetic north are only gradually moving across Britain, at this point, it’s only the far south west being affected. In Snowdonia, you would still be able to use the reminder from your army days to operate.

      Many thanks

  16. Christopher Fairfowl

    A little off piste I know but I have a Brunton pocket Transit – or at least it looks like a Brunton, and compared to 4 other compasses (all of which point in the same direction) it points 5 degrees East? I checked this in other locations as isolated as I can get it so to my knowledge there is no interference otherwise the others would be affected too.

    It has an adjustable bezel to adjust for declination but the needle doesn’t point North. The needle looks a little over complicated to me, it has a couple of small round pins running parallel to the needle and I’m wondering if one of these has moved and is “pulling” the needle off.

    Anyone got a clue as to what’s going on? any ideas?


  17. Andrew

    So I have just used the BGS website to calculate variance in Snwodonia and is says Mag is 0 degrees 55 mins West of Grid nowrth. appologise if I am being thick but this means that I when doing from Mag to grid I would have to add not get rid as the rhyme goes correct!?

    1. Hi Andrew

      Anything to the west of grid north still works with the old rhyme. It’s the far reaches of Cornwall that are seeing the shift to east of grid north at the moment, although it will gradually spread across GB – and then the rhyme will cease to work.

      Thanks, Gemma

  18. Pingback : It’s Not Just People Going Walkabout. | DPA

  19. Mike

    Why is True North shown on OS Maps? Surely it is irrelevant as we are only making adjustments between Grid and Magnetic norths for navigation. It would be simpler to only have 2 Norths to consider.

Leave a Reply

Your email address will not be published. Required fields are marked *

Name* :

Email* :