https://www.explainxkcd.com/wiki/api.php?action=feedcontributions&feedformat=atom&user=2A02%3AAA10%3AEA7E%3AED00%3A1DB7%3ADAC7%3A1294%3ADBB6explain xkcd - User contributions [en]2026-04-09T09:20:47ZUser contributionsMediaWiki 1.30.0https://www.explainxkcd.com/wiki/index.php?title=3207:_Bad_Map_Projection:_Zero_Declination&diff=4065783207: Bad Map Projection: Zero Declination2026-02-19T01:37:58Z<p>2A02:AA10:EA7E:ED00:1DB7:DAC7:1294:DBB6: /* Explanation */ + orienteering maps</p>
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<div>{{comic<br />
| number = 3207<br />
| date = February 13, 2026<br />
| title = Bad Map Projection: Zero Declination<br />
| image = bad_map_projection_zero_declination.png<br />
| imagesize = 740x544px<br />
| noexpand = true<br />
| titletext = 'The zero line in WMM2025 passes through a lot of population centers; I wonder what year the largest share of the population lived in a zone of less than 5° of declination,' he thought, derailing all other tasks for the rest of the day.<br />
}}<br />
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==Explanation==<br />
{{incomplete|This page was created recently by a misaligned map. Don't remove this notice too soon.}}<br />
This is the tenth comic in the [[:Category:Bad Map Projections|Bad Map Projections]] series, displaying Bad Map Projection #216: Zero Declination.<br />
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While the Earth's magnetic field is broadly aligned North-South, the actual alignment of the magnetic field varies over time and position. The difference between True North (the axis of Earth's rotation) and Magnetic North (the direction a compass will point) will vary depending on your position, and is known as the {{w|Magnetic Declination}} of that point.<br />
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The comic shows a map that has been distorted based on the Magnetic Declination so that Magnetic North for every point is pointed toward the top of the map. If this were reality, then Magnetic North would always be aligned with True North, or in other words, there would be Zero Declination at all points. <br />
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The red arrows indicate the distortions from the starting map required to make Magnetic North be at the top.<br />
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In the title text, "WMM2025" refers to the 2025 version of the {{w|World Magnetic Model}}, a representation of the Earth's magnetic field. You can see it [https://web.archive.org/web/20260212034745/https://www.ncei.noaa.gov/sites/default/files/inline-images/D.jpg here]. The "zero line" is in green, which shows where in the world magnetic declination is 0°. [[Randall]] has presumably wasted a day trying to figure out what year has had the most population living in an area of less than 5° declination by searching through previous WMM maps. He appears to have not found the answer, but luckily explainxkcd user Ahogue [[356|finished the job]] and made a [https://awhogue.github.io/zero-declination/output/ beautiful interactive map] to let you see that the answer is 2000.<br />
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You can see magnetic declination [https://www.ncei.noaa.gov/maps/historical-declination/ historical data here].<br />
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In {{w|orienteering}}, the maps are printed in such a way that magnetic north is always up - but given that the maps rarely show more than a few square kilometers, Randall's problem of mapping the entire world doesn't occur.<br />
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==Transcript==<br />
{{incomplete transcript|Don't remove this notice too soon.}}<br />
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{{comic discussion}}<noinclude><br />
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[[Category:Comics with red annotations]]<br />
[[Category:Bad Map Projections]]<br />
[[Category:Comics with color]]</div>2A02:AA10:EA7E:ED00:1DB7:DAC7:1294:DBB6