3207: Bad Map Projection: Zero Declination

Bad Map Projection: Zero Declination

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Title text: '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.

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Explanation

This is one of 65 incomplete explanations: This page was created recently by a misaligned map. Don't remove this notice too soon. If you can fix this issue, edit the page!

This is the tenth comic in the Bad Map Projections series, displaying Bad Map Projection #216: Zero Declination.

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 Magnetic Declination of that point.

The comic shows a map that has been distorted based on the Magnetic Declination such 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.

The red arrows indicate the distortions from the starting map required to make Magnetic North be at the top.

In the title text, "WMM2025" refers to the 2025 version of the World Magnetic Model, a representation of the Earth's magnetic field. You can see it here. The "zero line" is in green, which shows where in the world magnetic declension 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° declension by searching through previous WMM maps. He appears to have not found the answer, so explainxkcd requests its readers to finish the job.

Transcript

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Discussion

First! Can't believe I'm north! King Pando (talk) 03:34, 14 February 2026 (UTC)

What do you mean that you're north? This isn't a good name (talk) 03:42, 14 February 2026 (UTC)

You’re north, I’m fourth :) Logalex8369 (talk) 04:53, 14 February 2026 (UTC)

Hi fourth! i'm John 45.178.1.151 05:31, 14 February 2026 (UTC)

Hi John, I'm Dad. --DollarStoreBa'al^Converse (BLM) 11:32, 14 February 2026 (UTC)

I can't figure out what the red arrows are. My best guess is that they indicate the direction that the map was distorted in that area. It would be good if somebody would explain. Jordan Brown (talk) 04:07, 14 February 2026 (UTC)

I think you are right. here's a rough (map comparison) Sameldacamel34 (talk) 05:41, 14 February 2026 (UTC)

I thought it might be showing where things are drifting on the map with the current drift of the north pole. 2A02:3103:4C:2400:E259:E2C3:5BDD:1111 10:16, 14 February 2026 (UTC)

Wouldn't such a map actually be quite useful to anyone using only a compass to navigate? 2A06:C701:46AF:2C00:7577:585:1183:EFBD 07:37, 14 February 2026 (UTC)

I'm confused by the cylindrical projection used for this. I would have expected him to use the geomagnetic dipole for the projection axis, but this would put Ellesmere Island at the top of the map, which is clearly incorrect. Instead he seems to have used the geometric axis for the projection (or maybe the axis between magnetic dip poles, which would be similar in 2025?). This joke would have been better 20 years ago when the dip pole was solidly in Canada. Quantum7 (talk) 08:35, 14 February 2026 (UTC)

I've honestly seen worse "earnest" attempts at map projections. I might use this in the future just to see if anyone even notices. 2A00:FBC:F004:3364:B820:80FF:FEA3:938D

I see the zero line goes more or less through the Rift Valley in East Africa. If the same thing happened a couple of million years ago, it's quite likely every individual in the genus Homo once lived within a couple of degrees of declination.2A03:E600:100:0:0:0:0:10 14:53, 14 February 2026 (UTC)
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