More Fun with Cartography

Seems to be a month of map projections on here. Anyway, I’d like to spare a few more thoughts on gnomonic map projections, prime meridians, and the land and water hemispheres.

Of Map Projections Gnomonic

You might be asking “wait, what’s a gnomonic map projection?” I myself barely know a gnomon from a garden gnome, and aesthetically it’s far from my most favorite projection, but gnomonic maps do have one freaky property: any straight line drawn on them is a great circle! On a gnomonic projection if you draw a straight line between any two points, it is in fact the shortest route.

Great circles, as you might recall, are the shortest routes between two points on the Earth’s spherical surface, which over long distances arc in a curve relative to maintaining a constant compass direction (known as a “rhumb line” or a loxodrome), which always appears as a straight line in the Mercator projection; indeed, as I understand it the gnomonic and the Mercator are the two fundamental projections used for navigational purposes, the former for great circle routes and the latter for rhumb routes.

The downside (there’s always a downside…) to the gnomonic is twofold: first, distortion increases rapidly as one moves away from the central point on the map, and second, gnomonic projections can show at most one hemisphere, i.e. half of the world. Nevertheless, they do have a unique quality to them. Get a load of this 1943 publication I found on Reddit which featured a gnomonic map covering most of the northern hemisphere, whose author seemed to be under the impression that the gnomonic projection was the wave of the future, considering how air travel was incipient and great-circle routes would soon attain unprecedented relevance, perhaps even become the primary way we navigated.

You might assume a map projection as freaky and futuristic as the gnomonic was some triumph of modern science, but you’d be wrong! It’s actually literally the oldest known map projection, first developed by Thales for star maps in the 6th century BC. Those ancient Greeks did stuff with geometry that nobody else had even heard of…

Gnomonic maps centered on the north pole, the equator, and the 45th parallel. Notice that meridians always appear as straight lines; this is because meridians are by definition great circles. Like I said, freaky, isn’t it?

Prime Meridians: Why London?

Well, because British Empire, that’s why. Also the Greenwich Observatory being located there made it a convenient choice for the arbitrary designation of zero degrees longitude. Nevertheless, it is a bit odd in my opinion that a much better possibility was eschewed: the “Ferro Meridian”, the longitude of the westernmost point of El Hierro, the westernmost point of the world known in antiquity, which indeed was the most often used prime meridian by cartographers before the late modern period.

Advantages of El Hierro over Greenwich included the fact that the location was comfortably westward of the westernmost points of both Africa and Europe, meaning the entire continental landmass of Europe and Africa would enjoy positive longitude numbers, which in my view makes more sense. It’s 18 degrees west of the Greenwich meridian, and the prime antimeridian is shifted correspondingly 18 degrees westward, so instead of (what’s now called) 180 degrees east, which passes through the easternmost part of Chukotka, the antimeridian would run at (relative to the Greenwich meridian) the 162nd meridian east. The net effect is that Chukotka is located comfortably in the western hemisphere, along with the easternmost part of Kamchatka; New Zealand along with basically all of Polynesia is now in the western hemisphere.

Over on the other side of the world, by the way, no important landmasses are intersected by the El Hierro meridian, but Iceland is bisected by it, so it would straddle the western and eastern hemispheres; a very small portion of northeastern Greenland would be in the eastern hemisphere. Overall it would seem to work considerably better.

While changing our whole longitude system would hardly be worth it at this point, it’s worth noting there’s nothing stopping cartographers from centering world maps somewhere other than at or near the Greenwich meridian. It seems like it used to be common (e.g. in the WWII era) for world maps in the United States to center the Americas or the Pacific Ocean, yet now almost all world maps you see center Britain. If anything I believe it would make more sense to center the Pacific, in such a way as to cut off the world not at the Bering Strait but rather at the El Hierro meridian, so as to place the Old World on the left side of the map and the New World on the right side of the map, emphasizing (a la the Dymaxion map) the near-connection between the two in the Bering Sea area (not to mention trans-Pacific connections) as opposed to the Atlantic sea routes.

The world centered on Kamchatka

Land and Water Hemispheres

Another item of cartographic interest is the concept of the “land hemisphere” and the “water hemisphere”. The land hemisphere is the half of the Earth that contains the greatest possible percentage of land. This hemisphere is centered near France and contains 53 percent water and 47 percent land. Notice how 80 percent of the Earth’s land, and an even greater share of the population, are in the land hemisphere.

Image by Citynoise of Wikimedia Commons. CC-BY-SA 4.0.

I think the fact that most of us, for obvious reasons, live in the hemisphere containing the most land kinda blinds us to how vast the seas truly are and just how much of our planet’s surface is covered in water. From our point of view we might get an intuition that the distribution of land and sea is relatively even…which it is…in the land hemisphere. But by definition the opposite hemisphere, centered near New Zealand (antipodal to France) is the one that contains the most water, and hoo boy! The water hemisphere contains only 20 percent of the Earth’s land area but the majority of the oceans; perhaps more strikingly, it’s not 53 percent water but a full 89 percent water. Look at all that blue…

Image by Citynoise of Wikimedia Commons. CC-BY-SA 4.0.

In terms of human geography it gets even worse; nearly half of the water hemisphere’s land area is accounted for by Antarctica, meaning only about 5 percent of the water hemisphere’s area is dry land. Maritime Southeast Asia is the only truly major population center in the water hemisphere; notice how Australia and the southern cone of South America, the other two major dry landmasses, are sparsely populated. This despite having enormous potential; their remoteness from the centers of the land hemisphere, and their relatively more recent arrival on the global stage accounts for this discrepancy.

Another interesting discrepancy is how the center of the land hemisphere, where if all lands were equally populated would be one and the same as the center of population, is in France yet the actual center of population is in the Hindu Kush, thousands of miles eastward! This is of course primarily because of the enormous population densities in East and South Asia compared to other parts of the world.


Anyway, those are my somewhat scattered but I hope really interesting thoughts on some topics related to map projections, cartography, and the like. This stuff does make you think, doesn’t it? Look deeply enough into the abyss of maps and the abyss will gaze also back into you, hopefully imparting a whole new view of our world in the process. Such is the magic of scratching the surface of the plain ordinary world map you might have on your living room wall.

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