# What's the dryest great circle on Earth?May 10, 2007 7:12 PM   Subscribe

Which great circle on the Earth has the largest proportion of its length lying on land (not water)?
posted by Wolfdog to Science & Nature (23 answers total) 5 users marked this as a favorite

Greates proportion? Antarctica. It's pretty much solid below the 70th parallel, according to this pic.
posted by lekvar at 7:19 PM on May 10, 2007

Considering the essentially infinite number of great circles, I'm not sure how one go about figuring this out. It would almost have to be one that goes across as much of Asia as possible, though.
posted by cerebus19 at 7:22 PM on May 10, 2007

lekvar: A great circle has to have the same diameter as the Earth.
posted by cerebus19 at 7:22 PM on May 10, 2007 [1 favorite]

It wouldn't be too hard to take a image map of the world (converted to B&W for land and sea) and write an algorithm to compute the percentage of land on a given great circle (given 2 coords). Then write a search/optimization code to find the "dryest" great circle.
posted by jpdoane at 7:28 PM on May 10, 2007

posted by lekvar at 7:34 PM on May 10, 2007

As a computational problem, you'd have a lot of great circles to test. Practically an infinitely many for a given coordinate pair (of which there are also many), unless your scale is very large and the rotation is coarse. Sounds like an interesting problem.
posted by Blazecock Pileon at 7:41 PM on May 10, 2007

Isn't there that place in Xinjiang or somewhere in the far west of China that's supposedly the farthest from the sea? Presumably a circle drawn centring on that of a radius equal to that distance from the sea would be yer man.
posted by Abiezer at 7:57 PM on May 10, 2007

Whoops. I see I just made lekvar's mistake.
posted by Abiezer at 7:58 PM on May 10, 2007

Looking at Google Earth, it looks like you can cut through Antartica, South & North America, and a good chunk of east Asia, for maybe 70% land coverage. Now to find a globe nearby and a tape measure...
posted by ldenneau at 8:04 PM on May 10, 2007

My sig other sent me this link to give you guys: Duramater. I don't even usnderstand the question, so let me know, did this answer it?
posted by thebrokedown at 8:07 PM on May 10, 2007 [1 favorite]

Offhand, I'd say you can probably rule out any great circle that crosses the Atlantic or Pacific. I would guess it's something that's primarily North-South and goes through Africa/Europe and/or N. and S. America....

I think what Blazecock Pileon meant (unless I'm being stupid) is that for any point, there's an infinite number of great circles (rotating about that point), and there are an infinite number of points.

Of course, something integrated (like length under a particular great circle) will tend to have local maxima, so you can probably start with a coarse "grid" of points and do a coarse search of great circles for each. From this collection of local maxima, choose the few largest, and then look for an absolute maximum. Perhaps someone else will have a useful data set or a better algorithm.
posted by JMOZ at 8:10 PM on May 10, 2007

Won't there be only one line per coordinate pair, unless the coordinates are exactly opposite from each other, in which case there would be infinite lines?
posted by Kwantsar at 8:30 PM on May 10, 2007

err, pair of pairs.
posted by Kwantsar at 8:40 PM on May 10, 2007

The one that runs for its longest distance through Australia, where it rotates clockwise.
posted by Clyde Mnestra at 8:42 PM on May 10, 2007

thebrokedown: Step in the right direction. That post gives the longest paths over land and water that are parts of great circles; we're looking for the entire circle with the largest proportion over land. And 'great circle' is really just the equivalent of 'straight line' when you're working on the surface of a sphere: It's a circle as big as the sphere itself is.

Clyde Mnestra: Waitaminnit, Australia rotates?
posted by eritain at 9:42 PM on May 10, 2007

somewhere through afrlica over the poles?
posted by longsleeves at 10:13 PM on May 10, 2007

Start in Antarctica, go up through Argentina, Chile, Peru, Ecuador, all of Central America, the Yucatan, Texas to Montana, British Columbia, Alaska, Russia, China, Vietnam, Malaysia, Indonesia, then through the south Indian Ocean back to Antarctica.
posted by JackFlash at 11:07 PM on May 10, 2007

Here is a map that roughly gives the route I described above connecting Quito, Ecuador to Saigon, Vietnam. It needs to be tweaked slightly to cover more land, but that is the best I could do using airports on this mapping program. The southern half is shown in this map.

Don't be fooled by the appearance of the distance from the western edge of Africa to the eastern edge of Russia. That is a distortion of the map and the distance is actually shorter than the one shown in red and is not actually a great circle, if you look at a globe.
posted by JackFlash at 12:10 AM on May 11, 2007

thebrokedown has it!
posted by phrontist at 12:29 AM on May 11, 2007

The Vietnam-Senegal route that thebrokedown links to gives the longest single land segment which lies on a great circle, but it does not give the complete great circle with the most land.
posted by JackFlash at 1:03 AM on May 11, 2007 [1 favorite]

If ever a question needed a more inside.

Why, exactly, do you want to know this? I'm burning with curiosity.
posted by Deathalicious at 8:59 AM on May 11, 2007

here is a KML file showing the great circles with the most land, land+ice, and ocean.
posted by arialblack at 11:57 AM on May 12, 2007

Best answer, faved, and flagged as fantastic. But I won't name my children after you unless you disclose how you arrived at these.
posted by Wolfdog at 12:17 PM on May 12, 2007

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