Longest Straight Line Paths on Water or Land on the Earth (2018)

[−]ventana · 2026-08-30 Sun 08:44 UTC · link

The paper is basically like this (spoiler alert):

“Some random user on Reddit posted a picture claiming that this is the longest straight line path on water possible on the Earth. We implemented a smart algorithm to solve this problem, found the elevation data, ran our algorithm... yes, that random user was right. Also, here's the longest path on land.”

Thanks, I really enjoyed reading it, even though I hoped that they would disprove the original claim!

Edit: here are the gcmap links to the two paths: sea [1], land [2].

[1]: http://www.gcmap.com/mapui?P=25%B017%27N+66%B040%27E-58%B037...

[2]: http://www.gcmap.com/mapui?P=24%B033%27N+118%B038%27E-37%B02...

[−]comrade1234 · 2026-08-30 Sun 10:12 UTC · link

I opened Apple Maps in globe mode and I still have trouble visualizing the water path.

[−]pdpi · 2026-08-30 Sun 10:38 UTC · link

Does it help to point out that the water path looks suspiciously like the day/night line on a map?

Like this: https://svs.gsfc.nasa.gov/5477/

[−]newtwentysix · 2026-08-30 Sun 12:28 UTC · link

yes!! why is that ? :)

[−]yorwba · 2026-08-30 Sun 13:01 UTC · link

The day/light line is a great circle. The "straight line paths" are great-circle segments.

[−]srean · 2026-08-30 Sun 12:44 UTC · link

It's going South and then trying to close the loop from behind. It gets interrupted by land before the loop closes.

Hope it makes sense.

[−]turbocon · 2026-08-30 Sun 12:53 UTC · link

Open the linked paper and scroll down, they have images of the path on a globe as well as the flat map view.

[−]cubefox · 2026-08-30 Sun 11:13 UTC · link

They only identify the Reddit user as "kepleronlyknows", but in the Reddit thread [1] he links to his video visualization [2], where his user name is Patrick Anderson.

Before he made the video visualization using Google Earth, he actually went to the library and used a string on a real globe. [3]

1: https://www.reddit.com/r/MapPorn/comments/15mwai/the_longest...

2: http://www.youtube.com/watch?v=VpQwuGueeoA

3: https://imgur.com/a/great-circle-2hYFM

[−]shrx · 2026-08-30 Sun 09:21 UTC · link

> Figure 9: Longest Drivable Straight Line Path on Earth.

Walkable, maybe, but definitely not drivable (it crosses directly over the Alps, for example).

[−]pbhjpbhj · 2026-08-30 Sun 09:38 UTC · link

There might be icebergs or sandbars or rocks or volcanic activity or wars blocking the sailing route too. They seem like equivalents.

The longest mettled straight route with minimal deviation would also be an interesting exercise.

[−]kakacik · 2026-08-30 Sun 10:02 UTC · link

Extremely highly inprobable vs 100% there and directly impassable unless walking & doing some proper alpinism is hardly equivalent

[−]mikeaskew4 · 2026-08-30 Sun 12:15 UTC · link

Presume for a moment that you don’t drive on tyres…

[−]dr_dshiv · 2026-08-30 Sun 09:29 UTC · link

If it is undrivable in a straight line, why does that count? I’d assume the longest you could drive in a perfectly straight line would either be the longest straight highway or some drivable desert.

[−]loloquwowndueo · 2026-08-30 Sun 13:48 UTC · link

“Drive”.

Use your feet, car centric person.

[−]mrgriscom · 2026-08-30 Sun 09:42 UTC · link

I made a "first person" perspective rendering of this: https://mrgris.com/img/landfall/longest.png

[−]paufernandez · 2026-08-30 Sun 09:53 UTC · link

Nerd sniping at its best... ;)

[−]OscarCunningham · 2026-08-30 Sun 10:02 UTC · link

There's a longer land path that starts in or near Senegal and ends in China. But they miss it because it goes near the Dead Sea, and they treat anything below sea level as water.

[−]cubefox · 2026-08-30 Sun 11:14 UTC · link

That would an interesting finding!

[−]Anduia · 2026-08-30 Sun 12:06 UTC · link

If you are talking about the trail from Cape Town to Vladivostok, that one is not a straight line.

[−]evanb · 2026-08-30 Sun 12:33 UTC · link

They aren't, as clicking through on a sibling's link demonstrates. Moreover, Senegal is nowhere near Cape Town.

[−]maratc · 2026-08-30 Sun 12:11 UTC · link

Indeed, this route would be about 13,250 km, or about 2,000 km longer than the one TLA suggests.

http://www.gcmap.com/mapui?P=10%B0+24%27+41.4%22+N,+14%B0+31...

Or, using nearby airports: https://www.greatcirclemap.com/?routes=gucy-vmmc

[−]khaled_ismaeel · 2026-08-30 Sun 13:04 UTC · link

It seems like that path crosses the Suez canal. I think it's fair that bridges and/or tunnels don't count.

[−]Vvector · 2026-08-30 Sun 13:37 UTC · link

I'm confident that the Land Paths need bridges to cross the numerous rivers along the route. You need a different qualifier.

[−]OscarCunningham · 2026-08-30 Sun 15:39 UTC · link

The one they give also crosses numerous rivers and lakes. For the strict version of the challenge where you literally can't cross water it's likely that the best solution is across Antarctica. Guaranteed by temperature to contain no water whatsoever.

[−]hidroto · 2026-08-30 Sun 15:53 UTC · link

technically Antarctica is covered in (solid) water.

"technically incorrect the worst kind of incorrect".

[−]metalman · 2026-08-30 Sun 10:16 UTC · link

it would be interesting if it was a list of actual journeys with the sub lists of deviations required. a special club for the brutaly determined and persistant the "strait liners" things like having to beg, bluff, bribe, your way through someones house

[−]shrx · 2026-08-30 Sun 10:34 UTC · link

Wikipedia has an article listing some of the notable (walking) straight line missions: https://en.wikipedia.org/wiki/Straight_line_mission

edit: and the article already notes this longest possible path from Portugal to China, citing a 2023 article: https://bigthink.com/strange-maps/these-are-the-worlds-longe...

[−]fhars · 2026-08-30 Sun 11:59 UTC · link

Note that the 2023 article also cites the submission, which is five years older.

[−]1313ed01 · 2026-08-30 Sun 10:43 UTC · link

But what would flat-earthers consider the longest possible paths to be? Not the ones shown in the article, presumably?

[−]madcaptenor · 2026-08-30 Sun 12:17 UTC · link

Over water, probably something like the entire 60th parallel south.

Over land, I think you want to start near the westernmost point of the African continent and thread the needle of the Isthmus of Suez, and stay south of the Caspian Sea. At least in the projection gcmap.com uses (plate carree - essentially the x-coordinate and y-coordinate are just raw longitude and latitude), this keeps you south of Lake Baikal and allows you to get very far east in far eastern Russia. Something like 17.5 N, 16 W to 69 N, 178.5 E seems to work:

http://www.gcmap.com/mapui?P=17.5n16w-21.79n0.21e-26.08n16.4...

Of course this depends on the projection you use!

This is different from the Portugal-to-China path that is the longest over land in reality, which a flat-earther would have crossing the Mediterranean.

[−]Anduia · 2026-08-30 Sun 13:33 UTC · link

Flat earthers don't use Mercator projection, they use polar azimuthal equidistant (AEQD) projection centered in the north pole.

I think it would be something like Portugal-Kamchatka:

https://i.ibb.co/9mqz8fvb/image.png

[−]madcaptenor · 2026-08-30 Sun 13:55 UTC · link

I didn't know that. Makes more sense than a rectangular projection at least.

[−]1718627440 · 2026-08-30 Sun 14:01 UTC · link

> Of course this depends on the projection you use!

But if you do not believe in a globe how do you understand projections?

[−]Anduia · 2026-08-30 Sun 13:27 UTC · link

It would be a straight line (in their official map) from the south of Portugal to Kamchatka (east Russia)

[−]astrobe_ · 2026-08-30 Sun 15:19 UTC · link

They would tell us we are contradicting ourselves because none of them are straight lines in the traditional sense, if we really believe the Earth is a sphere. Don't underestimate trolls ;-)

[−]rotringlvr · 2026-08-30 Sun 13:04 UTC · link

Before I opened the solution, I knew it had to pass through the beagle straight. It is the only choke point separating the largest oceans, about both their empties areas, the far south.

I guess my biggest surprise is that there is a straight line through the Beagle straight.

[−]gus_massa · 2026-08-30 Sun 14:51 UTC · link

Beagle Channel is very narrow and has islands both on the north and the south. This path goes thought the Drake Passage that is south of the islands that are south of the Beagle Channel. The Drake Passage is very wide.

[−]joebig · 2026-08-30 Sun 13:14 UTC · link

I myself walked the longest path to 1200 karma. It was painful. Blisters of delta_karma=f*vote_points, where f could be 0.5 or 0.3 or unknown lower no. I'm tired, boss.

[−]trencedamp · 2026-08-30 Sun 13:50 UTC · link

If it's the longest straight path on water OR land then surely it's just the circumference of the earth

[−]mdritch · 2026-08-30 Sun 13:55 UTC · link

It reminds me of a bit I did a few years ago trying to find the "longest straightest" line in Atlanta [PDF]: https://matthewritch.com/pages/LongestStraightestLine.pdf

[−]gcanyon · 2026-08-30 Sun 14:24 UTC · link

I know the globe is unintuitive (it still blows my mind that Muslims in New York City face roughly northeast to point toward Mecca) but it still seems bizarre that the water route can start near the arctic circle, cross the Pacific ocean, nearly touch Antarctica, cross the Atlantic ocean, and cross the Indian ocean to end well north of the equator and still travel only 80% of the way around the globe. This view of the rest of that great circle helped me visualize it: http://www.gcmap.com/mapui?P=58%B037%27N+162%B014%27E-25%B01...

[−]hnx0rqy49u · 2026-08-30 Sun 14:50 UTC · link

Learned this the expensive way

[−]divbzero · 2026-08-30 Sun 15:32 UTC · link

This geographic puzzle feels like the modern day version of the Seven Bridges of Königsberg:

https://en.wikipedia.org/wiki/Seven_Bridges_of_Königsberg