# Mercator projection: why aren't parallels equidistant?

**URL:** <https://boards.straightdope.com/t/mercator-projection-why-arent-parallels-equidistant/90960>\
**Category:** Factual Questions\
**Created:** [November 1, 2001, 6:37pm UTC](https://boards.straightdope.com/t/mercator-projection-why-arent-parallels-equidistant/90960 "2001-11-01T18:37:51Z")\
**Posts on this page:** 4\
**Page:** 2

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**Author:** ![Timz](https://avatars.discourse-cdn.com/v4/letter/t/6a8cbe/32.png) [@Timz](https://boards.straightdope.com/u/Timz)\
**Post date:** [July 30, 2025, 4:43pm UTC](https://boards.straightdope.com/t/mercator-projection-why-arent-parallels-equidistant/90960/21 "2025-07-30T16:43:45Z")

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A degree of latitude is 1% longer at the poles than at the equator.

The point of the two expeditions was to decide whether the Cassinis were right, that Earth’s north-pole-to-south-pole distance was greater than its equatorial diameter. Wonder why they thought that.

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**Author:** ![JKellyMap](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jkellymap/32/15880_2.png) [@JKellyMap](https://boards.straightdope.com/u/JKellyMap)\
**Post date:** [August 18, 2025, 9:55pm UTC](https://boards.straightdope.com/t/mercator-projection-why-arent-parallels-equidistant/90960/22 "2025-08-18T21:55:20Z")

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Correct.

I know you know this, but to clarify: a coordinate system is not a projection. I wouldn’t even call it a “map projection system,’ as that Wikipedia author did. It’s a coordinate system.

(The UTM coordinate system happens to use a particular projection, used in a particular way, while at least one coordinate system – the well-known latitude-longitude one – doesn’t use a projection at all; some call it a “geographic” coordinate system, as opposed to UTM’s “projected” one).

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**Author:** ![Wendell\_Wagner](https://avatars.discourse-cdn.com/v4/letter/w/8491ac/32.png) [@Wendell\_Wagner](https://boards.straightdope.com/u/Wendell_Wagner)\
**Post date:** [August 18, 2025, 10:08pm UTC](https://boards.straightdope.com/t/mercator-projection-why-arent-parallels-equidistant/90960/23 "2025-08-18T22:08:53Z")

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> [@sailor](#):
>
> If i own a plot of land in Washington DC which is rectangular and 1’of latitude wide by 1’of longitude wide, I do not have a square piece of land as it is longer in the N-S direction.

Yes, but it is just off the islets of Langerhans.

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**Author:** ![Johanna](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johanna/32/8318_2.png) [@Johanna](https://boards.straightdope.com/u/Johanna)\
**Post date:** [August 27, 2025, 2:45am UTC](https://boards.straightdope.com/t/mercator-projection-why-arent-parallels-equidistant/90960/24 "2025-08-27T02:45:15Z")

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[At 2nd and H Street Northeast, to be precise](https://en.wikipedia.org/wiki/Adrift_Just_Off_the_Islets_of_Langerhans). I read that story too. Or tried to.

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