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...

The Portugal to (approximately) Macao one is quite interesting, thanks for the links!

Adding: The two paths respectively are about 80% and 28% of the earth's circumference.

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

Kudos to whoever built tiled clouds background on the gcmap site.

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

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/

yes!! why is that ? :)

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

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.

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

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.

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

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

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.

technically Antarctica is covered in (solid) water.

"technically incorrect the worst kind of incorrect".

> Guaranteed by temperature to contain no water whatsoever.

Depends on where and when.

Plenty of puddles form around the bases in summer.

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

In passing, https://en.wikipedia.org/wiki/Paul_Salopek is walking from Ethiopia to Tierra del Fuego, tracing the path of human migration out of Africa. Walking the coast, not a straight line.

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

That would an interesting finding!

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

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

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...

If you're in New York and you look due East across the Atlantic, what country are you looking at?

Most people would assume Portugal.

Nope, you're looking (over the curve of the earth, of course), at Morocco. Look just a tiny bit to the south and you're looking at the rest of West Africa. Look Southwest and you're looking at Australia, or even Brazil.

> it still blows my mind that Muslims in New York City face roughly northeast to point toward Mecca

It never occurred to me they would face the shortest distance to Mecca. I've looked it up and apparently it's a point of contention in North America, although the great circle seems to be standard. Interestingly there are landmasses around the antipode of Mecca, which means your direction would vary wildly as you travel around.

I like the idea of there being a place on land where a Muslim can look anywhere, and be looking toward Mecca.

But apparently, it's the middle of the ocean, although there does appear to be an atoll very close by: https://en.wikipedia.org/wiki/Tematagi

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

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

This is mathematics, the Alps is drivable like a manifold is smooth.

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

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

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

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

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

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.

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

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

> Of course this depends on the projection you use!

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

Well, they wouldn't call it a "projection", but whatever drawing of the map they use.

Yeah, but how do they explain, that the same world looks different, e.g. having different distances and angles depending on the map "type"? This is kind of important for traveling, navigating or measuring the size of the property you own.

They’re flat earthers, they either have no explanation or a completely bogus explanation. Certainly don’t look for any semblance of reason. They just invent whatever to try and feel like they have some secret knowledge.

I'm just curious. I think they still believe to have a consistent worldview themself, as every human does. My question was more regarding their self-understanding and less the kind-of "marketing" they throw at outsiders.

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 ;-)

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

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.

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.

Right, the Drake.

“Drive”.

Use your feet, car centric person.

Learned this the expensive way

Nerd sniping at its best... ;)

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

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...

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

Hi, ig?

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.