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What are meridian lines on a map4/14/2024 ![]() The changing direction of magnetic north is now approaching this ’magic line‘ so all three will briefly be in alignment. For the National Grid this central meridian line is 2°W or 400000m E. A transverse Mercator projection has a “central meridian” line where a chosen longitude aligns with a vertical eastings grid line. The amount of curvature varies across the grid area, except at one line. On a map projection like the transverse Mercator projection used for the British National Grid, the longitude lines curve away from the straight grid lines. This is the direction of lines of longitude that all converge at the north pole. ![]() Now, there is a third line about to come into alignment – true north. We wrote a blog on the progress of alignment between magnetic and grid north in Britain back in 2019, which you can read here. The change started in the very south-west corner of Britain and will slowly progress across the whole country over the next 12 to 13 years. ![]() In 2014, for the first time in Great Britain since the 1660s, magnetic north moved from being to the west of grid north to the east.
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