# lowest great circle constant altitude flight? **URL:** \ **Category:** Factual Questions\ **Created:** [September 10, 2014, 6:35pm UTC](https://boards.straightdope.com/t/lowest-great-circle-constant-altitude-flight/698100 "2014-09-10T18:35:55Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![cmosdes](https://avatars.discourse-cdn.com/v4/letter/c/a587f6/32.png) [@cmosdes](https://boards.straightdope.com/u/cmosdes)\ **Post date:** [September 10, 2014, 6:35pm UTC](https://boards.straightdope.com/t/lowest-great-circle-constant-altitude-flight/698100/1 "2014-09-10T18:35:55Z")
If I pick the right great circle route, what is the lowest constant altitude I can fly a plane and not run into a permanent structure? Is there a great circle route where the tallest structure (building, mountain, plateau, whatever) is below 1000’? My first thought is that it would be a predominantly North/South route that splits Alaska/Siberia and continued over the polar ice cap. Would that head over East Africa? Is there anything in the way that would significantly raise the minimum level? ---
**Author:** ![bump](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bump](https://boards.straightdope.com/u/bump)\ **Post date:** [September 10, 2014, 6:55pm UTC](https://boards.straightdope.com/t/lowest-great-circle-constant-altitude-flight/698100/2 "2014-09-10T18:55:57Z")
Here you go. [http://www.gcmap.com/mapui?P=NZWD-PAWD%2C+&PM=b%3Adisc7%2B%25U&MS=wls&DU=mi&E=180](http://www.gcmap.com/mapui?P=NZWD-PAWD%2C+&PM=b%3Adisc7%2B%25U&MS=wls&DU=mi&E=180) McMurdo Sound to Seward, AK. 9692 nautical miles. ---
**Author:** ![cmosdes](https://avatars.discourse-cdn.com/v4/letter/c/a587f6/32.png) [@cmosdes](https://boards.straightdope.com/u/cmosdes)\ **Post date:** [September 10, 2014, 7:14pm UTC](https://boards.straightdope.com/t/lowest-great-circle-constant-altitude-flight/698100/3 "2014-09-10T19:14:42Z")
Let me clarify. I want a route that will circumnavigate the globe, but at the lowest possible constant altitude. Not to be done in a real plane, so fuel considerations and such are not included. ---
**Author:** ![GusNSpot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gusnspot/32/436_2.png) [@GusNSpot](https://boards.straightdope.com/u/GusNSpot)\ **Post date:** [September 10, 2014, 7:51pm UTC](https://boards.straightdope.com/t/lowest-great-circle-constant-altitude-flight/698100/4 "2014-09-10T19:51:33Z")
Without even a slight jig or jog? You have a globe? You can get to Google Earth? I’m just as lazy as anybody, so I do not put effort into … well, you get the idea. ---
**Author:** ![GusNSpot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gusnspot/32/436_2.png) [@GusNSpot](https://boards.straightdope.com/u/GusNSpot)\ **Post date:** [September 10, 2014, 7:57pm UTC](https://boards.straightdope.com/t/lowest-great-circle-constant-altitude-flight/698100/5 "2014-09-10T19:57:10Z")
Easy, circle Antarctica. Did not even have to look anything up. Oh, your definition of circumnavigate is that it must be cutting the Earth into equal halves, not have a bend in the line? Why did you not say so?? Why do you get to define ‘circumnavigate’ that way when everybody else who actually do circumnavigation don’t? Do I have to use True North or Can I use Magnetic North? I’m still not going to go do it for you. ---
**Author:** ![jtur88](https://avatars.discourse-cdn.com/v4/letter/j/e9c0ed/32.png) [@jtur88](https://boards.straightdope.com/u/jtur88)\ **Post date:** [September 10, 2014, 8:00pm UTC](https://boards.straightdope.com/t/lowest-great-circle-constant-altitude-flight/698100/6 "2014-09-10T20:00:23Z")
By “altitude”, do you mean above sea level, or above average terrain? What does “circumnavigate” mean – flying a light plane in a 100-meter circle around the north pole? ---
**Author:** ![buddy431](https://avatars.discourse-cdn.com/v4/letter/b/6a8cbe/32.png) [@buddy431](https://boards.straightdope.com/u/buddy431)\ **Post date:** [September 10, 2014, 8:09pm UTC](https://boards.straightdope.com/t/lowest-great-circle-constant-altitude-flight/698100/7 "2014-09-10T20:09:19Z")
He clearly said “great circle”, which yes, means flying a straight path, i.e. cutting the world into two equal parts. Is there any mapping software where you can pick two points arbitrarily and it will draw in the entire great circle? A globe would probably make this easiest ---
**Author:** ![bibliophage](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bibliophage/32/7615_2.png) [@bibliophage](https://boards.straightdope.com/u/bibliophage)\ **Post date:** [September 10, 2014, 8:09pm UTC](https://boards.straightdope.com/t/lowest-great-circle-constant-altitude-flight/698100/8 "2014-09-10T20:09:41Z")
Folks, circling the north pole or Antarctica won’t cut it because those routes aren’t [great circles](http://en.wikipedia.org/wiki/Great_circle). Any great circle that passes north-south through the Bering Strait will also cross over Antarctica. The ice sheet on most of Antarctica is typically 7000 to 10000 feet above sea level. Playing around on Google Earth, I found a route that looks like it doesn’t go over 4000 feet, though it gets close in 3 different places. I didn’t spend enough time at it to guarantee the route is exactly a great circle, nor that it never goes over 4000 feet. I make no claim that my route is the lowest possible, just the best I found in a half hour playing at it. It skirts Enderby Land in Antarctica (the coast nearest South Africa), crosses the lowlands of eastern Brazil, New England (possible highest terrain, three to four thousand feet), Hudson Bay, NWT and Yukon (another possible highest terrain), north of the Alaska Range, across the Pacific, western New Guinea (another possible highest terrain), Western Australia, and back to the origin. ---
**Author:** ![cmosdes](https://avatars.discourse-cdn.com/v4/letter/c/a587f6/32.png) [@cmosdes](https://boards.straightdope.com/u/cmosdes)\ **Post date:** [September 10, 2014, 8:13pm UTC](https://boards.straightdope.com/t/lowest-great-circle-constant-altitude-flight/698100/9 "2014-09-10T20:13:52Z")
> [@GusNSpot](#): > > Easy, circle Antarctica. Did not even have to look anything up. > > Oh, your definition of circumnavigate is that it must be cutting the Earth into equal halves, not have a bend in the line? Why did you not say so?? > Why do you get to define ‘circumnavigate’ that way when everybody else who actually do circumnavigation don’t? > > Do I have to use True North or Can I use Magnetic North? > > I’m still not going to go do it for you. I mentioned that I’m looking for a great circle route, so I was hoping people could combine “great circle” with “circumnavigate” and get to the realization this would indeed be a route that divides the Earth into two equal halves. So, to answer your question about why I didn’t say so, I thought I had with the OP. The second post did not circumnavigate the the earth, so I included that stipulation. Why is my definition of circumnavigate different than anyone else’s? I’m using it to mean going completely around the Earth. **jtur88** By altitude I mean above sea level. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [September 10, 2014, 8:39pm UTC](https://boards.straightdope.com/t/lowest-great-circle-constant-altitude-flight/698100/10 "2014-09-10T20:39:32Z")
> [@GusNSpot](#): > > Oh, your definition of circumnavigate is that it must be cutting the Earth into equal halves, not have a bend in the line? Why did you not say so?? The OP did say so. It says “great circle” right there in the thread title, and in the first sentence, and also in the 2nd sentence. And didn’t even use the term “circumnavigate” in the OP. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 10, 2014, 9:00pm UTC](https://boards.straightdope.com/t/lowest-great-circle-constant-altitude-flight/698100/11 "2014-09-10T21:00:23Z")
I once saw a great circle which is _almost_ entirely over ocean, basically around the edge of the South Pacific. The bits of land it does cross are probably pretty low, being near the ocean, but I don’t know the exact circle, nor the heights of the land. ---
**Author:** ![septimus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/septimus/32/410_2.png) [@septimus](https://boards.straightdope.com/u/septimus)\ **Post date:** [September 11, 2014, 2:29am UTC](https://boards.straightdope.com/t/lowest-great-circle-constant-altitude-flight/698100/12 "2014-09-11T02:29:10Z")
> [@bump](#): > > Here you go. > > [http://www.gcmap.com/mapui?P=NZWD-PAWD%2C+&PM=b%3Adisc7%2B%25U&MS=wls&DU=mi&E=180](http://www.gcmap.com/mapui?P=NZWD-PAWD%2C+&PM=b%3Adisc7%2B%25U&MS=wls&DU=mi&E=180) I was excited to see your link because I have my own great circle puzzles to solve. And was curious to personally [verify this great-circle related conspiracy theory](http://www.grahamhancock.com/phorum/read.php?f=1&i=174348&t=173765). But your site doesn’t actually show great circles – just segments of such circles. And asks for airport codes. Is there a way to use that site (or another) for what I want? ETA: The definition of circumnavigation has been considered here before: > [@How many miles to circumnavigate the Earth by boat?](https://boards.straightdope.com/t/how-many-miles-to-circumnavigate-the-earth-by-boat/615387/12): > > > [@How many miles to circumnavigate the Earth by boat?](https://boards.straightdope.com/t/how-many-miles-to-circumnavigate-the-earth-by-boat/615387/11): > > > > I think this is equivalent to my criterion, which is that at least one pair of points on the route be antipodal to each other. > > Yes, though come to think of it either definition would allow you to travel West from Ecuador to Singapore and then turn around, never visiting Indian or Atlantic Oceans. Adding the requirement “Visit every meridian” is insufficient since it allows you to start from Antarctica, circumnavigate the Arctic and come back, never visiting the Pacific. > > Back to the drawing board. :dubious: > > ETA: Perhaps the key is to intersect each great circle twice. :eek: ---
**Author:** ![MikeS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MikeS](https://boards.straightdope.com/u/MikeS)\ **Post date:** [September 11, 2014, 2:40am UTC](https://boards.straightdope.com/t/lowest-great-circle-constant-altitude-flight/698100/13 "2014-09-11T02:40:14Z")
Interestingly, the [longest great-circle segment entirely over the ocean](http://i.imgur.com/rQlk4.png) doesn’t help us with this; the remaining overland segment would have to cross the Himalayas. ---
**Author:** ![GusNSpot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gusnspot/32/436_2.png) [@GusNSpot](https://boards.straightdope.com/u/GusNSpot)\ **Post date:** [September 11, 2014, 5:37am UTC](https://boards.straightdope.com/t/lowest-great-circle-constant-altitude-flight/698100/14 "2014-09-11T05:37:37Z")
> [@cmosdes](#): > > Let me clarify. > > I want a route that will circumnavigate the globe, but at the lowest possible constant altitude. Not to be done in a real plane, so fuel considerations and such are not included. Boats do this all the time at 0 altitude. If you want a single great circle route, I don’t think there is one that does not gross some land. I agree with the 4000 ’ posted up thread. IMO, you can call a single great circle route a circumnavigation But a track that is always over water, like boats would do it may have several segments but you can’t say they did not do a circumnavigation… YMMV ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [September 11, 2014, 1:20pm UTC](https://boards.straightdope.com/t/lowest-great-circle-constant-altitude-flight/698100/15 "2014-09-11T13:20:37Z")
> [@Chronos](#): > > I once saw a great circle which is _almost_ entirely over ocean, basically around the edge of the South Pacific. Where does it go in the northern hemisphere? (All great circles - okay, all but one - have half their distance there.) ---
**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\ **Post date:** [September 11, 2014, 1:24pm UTC](https://boards.straightdope.com/t/lowest-great-circle-constant-altitude-flight/698100/16 "2014-09-11T13:24:11Z")
> [@GusNSpot](#): > > Boats do this all the time at 0 altitude. > > If you want a single great circle route, I don’t think there is one that does not gross some land. > > I agree with the 4000 ’ posted up thread. > > IMO, you can call a single great circle route a circumnavigation > > But a track that is always over water, like boats would do it may have several segments but you can’t say they did not do a circumnavigation… > > YMMV I think you are still missing the point. The OP quite clearly asked what is the great circle route that could be flown at the lowest altitude. No mention of circumnavigation. It’s a simple, and interesting question. ---
**Author:** ![PlainJain](https://avatars.discourse-cdn.com/v4/letter/p/5daacb/32.png) [@PlainJain](https://boards.straightdope.com/u/PlainJain)\ **Post date:** [September 11, 2014, 2:33pm UTC](https://boards.straightdope.com/t/lowest-great-circle-constant-altitude-flight/698100/17 "2014-09-11T14:33:29Z")
> [@GusNSpot](#): > > I’m still not going to go do it for you. No one’s asking you to. This is a message board where people come to discuss interesting ideas… like the OP, for example. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 11, 2014, 3:18pm UTC](https://boards.straightdope.com/t/lowest-great-circle-constant-altitude-flight/698100/18 "2014-09-11T15:18:07Z")
The route I was thinking of was the one which **MikeS** posted and then promptly eliminated. I was working from an imperfect memory, rather than from the picture which makes it clear it’s no good here. ---
**Author:** ![jtur88](https://avatars.discourse-cdn.com/v4/letter/j/e9c0ed/32.png) [@jtur88](https://boards.straightdope.com/u/jtur88)\ **Post date:** [September 11, 2014, 4:17pm UTC](https://boards.straightdope.com/t/lowest-great-circle-constant-altitude-flight/698100/19 "2014-09-11T16:17:59Z")
The term “great circle” has no applicability to circumnavigation. It is a navigational expression that differentiates a route on a curved surface from any route that follows lines of latitude or longitude. On a globe, a great circle is the shortest distance along the surface from any point A to B. If A and B are at the same place, a great circle would be a geometric circle of any circumference around any arbitrary point C, which could be an inch from the starting point, and 2-pi inches in circumference… I am assuming the OP is looking for a great circle that is defined as equal in length to the circumference of the earth. The question is meaningless if it allows for any smaller circumference. The term “great circle” is what is throwing us off, because that has a specific meaning in navigation that is not applicable here. The question should have been “Is there an undeviating line equal to the circumference of the earth that never passes through a point of relief above 1,000 feet above sea level?” Expressed as a hand-held model, is there a closed loop of string that fits tight over a globe such that it never passes over land of greater than 1,000 feet elevation. Imagining it in my mind, a candidate might be a circle that crosses the prime/ meridian near London, but deviates a bit southwesterly there to bypass the higher Sahara and the Antarctic continent, passing then up the Indian Ocean to the Bering Strait. ---
**Author:** ![Ravenman](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ravenman/32/2929_2.png) [@Ravenman](https://boards.straightdope.com/u/Ravenman)\ **Post date:** [September 11, 2014, 4:27pm UTC](https://boards.straightdope.com/t/lowest-great-circle-constant-altitude-flight/698100/20 "2014-09-11T16:27:12Z")
Geez, I feel like I’m one of the few people who understand the question. Imagine you take off from some point on the earth in an airplane, and travel 24,000 miles without turning left or right, so that you end up at the exact same spot on the earth. What route would allow you to accomplish this at the lowest possible altitude, and what is that minimum altitude? And no, you can’t deviate around mountains. [Next page](https://boards.straightdope.com/t/lowest-great-circle-constant-altitude-flight/698100.md?page=2)