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For those who navigate Great Britain's landscape by map and compass there are three norths.
Grid north is the direction of a grid line which is parallel to the central meridian on the National Grid, the reference system on Ordnance Survey maps.
True north is the direction of a meridian of longitude, an imaginary circle of the Earth, which converges on the North Pole.
Magnetic north is the direction magnetic compasses point to.
It is always shifting, very slowly, influenced by changes in the Earth's magnetic field which is itself affected by changes to the spinning of the planet's core.
For the first time in more than 220 years of map making, Ordnance Survey has noted that it lies east, and not west, of grid north for parts of southern Britain.
Generations of outdoor fans have grown up with the knowledge that, for accurate navigation using a compass, the housing has to be moved a few degrees to the West when using a bearing from the OS grid.
Now, in a small area of England west of Penzance, the grid magnetic angle is slightly to the East.
The reason is that the magnetic force that attracts a compass needle constantly moves and, relative to Great Britain, has been heading gradually eastwards for a few years.
http://www.bbc.co.uk/news/uk-scotland-highlands-islands-25841106http://www.grough.co.uk/magazine/2014/01/22/eastern-turn-for-compasses-for-first-time-in-200-years-as-north-shifts
Thanks Mr Swarfield
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