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xkcd #3207: Bad Map Projection: Zero Declination (imgs.xkcd.com)
submitted 9 months ago by [B] to c/xkcd@lemmy.world
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xkcd #3207: Bad Map Projection: Zero Declination

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.

Transcript:

Transcript will show once it’s been added to explainxkcd.com

Source: https://xkcd.com/3207/

explainxkcd for #3207

'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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[–] 25 points 9 months ago* (last edited 9 months ago) (4 children)

I don't think I have ever needed the ExplainXKCD more. I hope it's a good one.

Edit: Darn, it doesn't look any worse than Mercators to me.

Edit2: ExplainXKCD works while I sleep. Looks like @darkcloud@lemmy.world figured it out below as well.

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  • [–] 21 points 9 months ago* (last edited 9 months ago) (2 children)

    Magnetic north is variable, and curved. It's not even accross continents and changes over time. So the map is distorted so that up on the 2D plane of the drawing is magnetic north... Meaning all the countries and shapes are distorted so that magnetic north at those locations matches up in the drawing.

    They're drawn so that magnetic north is the top border of the image.

    I think the red arrows are pointing out how shapes are being deformed, because the changes are relatively subtle.

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    • [–] 2 points 9 months ago (1 child)

    Is this even a bad map projection? If you're working with a compass this sounds pretty useful

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    • [–] 1 point 9 months ago

    Scandinavia, Novaya Zemlya, and Taymyr Peninsula went all kinds of askew.

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