Daily Archives: May 7, 2020

Does this projection make my continent look big?

 I drew this version of Ptolemy’s map showing only the longitude lines. He drew them curved to give you the idea that the world is round.

A challenge navigators faced when reading a flat map of the round Earth is that as the meridians—the longitude lines—got closer to the north and south poles they kind of bent around to simulate the round globe. That’s a problem if you’re trying to chart a course. The meridians and parallels don’t meet at right angles so you need to keep adjusting your calculations about where you are…it’s a hot mess.

Gerard Mercator devised a way to mathematically flatten the globe. He imagined a flat map wrapped like a cylinder around the globe. So far, so good. But as you bend the top and bottom of the map to wrap the globe, they get all bunched up, right? There’s too much paper. So he trimmed some paper off the top and bottom, leaving strips that are wide at the Equator and pointy at the poles. These strips are called ‘gores’ in the cartography business.

Without Mercator, with Mercator.

You can do two things with these gores when you flatten them. One is to leave them as they are, with blank space in between the pointy ends. The other is to fill in the blank space in between the pointy ends with more map. Mercator did that— and he straightened the meridians and drew the continents to fit the new coordinates. The result is that you can use the latitude/longitude lines to chart a course that will be perfectly accurate.

Of course, the land and ocean at the top and bottom get stretched out on Mercator’s projection. That makes sense, because what had been a dot (the pole) has been stretched out across the top or bottom of the map.

Recently, some people have complained that on Mercator’s map, the continents closer to the poles appear to have more land mass than the continents near the Equator. That appearance has caused the residents of the equatorial countries to feel bad about their land mass.

The Western Civ User’s Guide staff is here to help. If you’re feeling bad about your land mass, call 1-800-IFEELBADABOUTMYLANDMASS and talk to one of our concerned and sympathetic counselors.

https://www.vox.com/2015/3/5/8151303/gerardus-mercator-maps
https://www.businessinsider.com/mercator-projection-v-gall-peters-projection-2013-12

https://www.britannica.com/science/Mercator-projection

Here’s a great old video of how globes are made. https://www.youtube.com/watch?v=4RWcWSN4HhI
Notice how when they paste the map onto the globe, the map is cut into sections called ‘gores’—pointy at top and bottom, wide in the middle.

http://gallery.lib.umn.edu/exhibits/show/maps-and-mapmakers–martin-wal/about_the_exhibit

Here’s the amazing 17-year-old Leslie Gore, who is not a section of a map. https://www.youtube.com/watch?v=RjdH_NmmO0I

Back to the beginning of The Western Civ User’s Guide to Time & Space