Magnetic North on the Move

One thing that many people don't realize when they're new to outdoor walking and navigation is that their compass doesn't point to grid north – except by coincidence in some areas¹. The compass needle is attracted by magnetic force, which varies in different parts of the world and is constantly changing.

When I was in the scouts the magnetic variation throughout Great Britain was typically about 8° west of grid north but the amount of variation changes every year. Indeed I've got old maps from when my Dad was a scout back in the 1940s and they show a variation of 15°!

For years the variation 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 and that change is slowly crossing the country as the magnetic north pole continues to migrate.

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

Anyway, what does all this mean in practical terms? Well actually it's rather good news. Even when I was a scout and the magnetic variation was 8° it was questionable as to whether it was worth worrying too much about accounting for it unless you needed to transfer a very exact bearing to/from a map as in the real world it's pretty difficult to walk in that straight a line but now we're drifting down towards zero there's a pretty strong case for simply not worrying about magnetic variation at all, at least for the next couple of decades or so!

1. And that's before we start worrying about the fact that grid north is not the same as true north, but let's not even go there!

Tagged: maps

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