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19th Jan 2010
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What are declination, grid, true and magnetic north?

TrackLogs Digital Mapping

Magnetic declination is the difference, in degrees, between grid and magnetic north. Grid north is indicated by a map grid, magnetic north is the direction indicated by a compass.

Ordnance Survey Declination in GB

When calculating the declination within Great Britain there are actually three norths to consider. This is because the Ordnance Survey grid is rectangular whilst the earth is round[1]. At the centre of the grid the northings (grid north) do point to the geographic north pole (true north). To the east and west the grid and true norths start to deviate. The direction pointed by a compass (magnetic north) varies across the country and is also changing over time. The total declination across Great Britain currently varies plus or minus a couple of degrees.

TrackLogs North

In TrackLogs we always display bearings using grid north. These will vary from compass readings by a couple of degrees depending on your location. If this matters to you then you should use a compass with declination compensation and set the compensation to the magnetic declination value in your area.

[1] Round'ish', it's actually elliptical.

Written by TrackLogs Digital Mapping. Copyright TrackLogs Digital Mapping 2002-2014. All rights reserved. Please send any comments, questions or feedback to support@tracklogs.co.uk


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