These are the world’s longest straight lines

Researchers use algorithms to find the longest straight-line distances on land and at sea

  • What links a small town in Portugal and a huge port city in China?
  • The answer may surprise even inhabitants of both places: the world's longest straight line over land
  • That line and its maritime equivalent were determined not by exploration but by calculation

What connects the Chinese port of Quanzhou with Sagres, a tiny parish in southern Portugal? No, it's not the New Silk Route, the Sino-European rail link inaugurated in 2017 (1). The answer is so arcane that it will surprise most inhabitants of either place: they are the extreme points of the world's longest straight line over land (2).

Following the course of that line would require directional rectitude of the highest degree. Travellers would have to forgo the relative comfort of well-worn roads and mountain passes and traverse daunting peaks and inhospitable deserts – not to mention innumerable private houses and public buildings.

Suggested route

Image: Reddit

Longest sailable straight line on Earth, as suggested by Reddit user kepleronlyknows.

They would cross 15 countries; skirting Madrid and Switzerland's alpine highlands; cutting off a corner of Austria and passing just north of Auschwitz in Poland; barely touching Ukraine and slicing through Belarus; travelling through Russia and Kazakhstan before hitting China and reaching the Formosa Strait; but not before dipping into Mongolia twice.

Because the globe is round and this map is not, the world's longest straight line over land – like all others long enough – looks like a bendy one on this image. For anyone walking the line, though, it would have been straight as a ruler, and, at the end of that trip, close to 20,000 miles long.

Threading the needle

Image: Chabukswar & Mukherjee

Algorithmically correct: the world's longest sailable straight line goes from Pakistan to Kamchatka

The world's longest straight line on land was calculated by researchers Rohan Chabukswar of the United Technologies Research Centre (UTRC) in Cork (Ireland) and Kushal Mukherjee at IBM's Research Laboratory in New Delhi (India).
In a paper published earlier this year (and last updated on 25 December), they set out their solution to the question of finding the world's longest straight lines over land and at sea. That question sounds simple enough, but isn't: "This is an optimisation problem, rendered chaotic by the presence of islands and lakes, and indeed the fractal nature of the coasts".

They were prompted by a map that had raised a lot of discussion since its first publication on Reddit in 2012. Posted by user kepleronlyknows, it purports to show the longest possible straight-line sailing route in the world: from Pakistan to Kamchatka, threading the needle twice – through the Mozambique Strait separating Madagascar from the African mainland, and via the Drake Passage between South America and Antarctica.

Walk this way

Image: Chabukswar & Mukherjee

A long walk indeed, but a straight one: Portugal to China

Commenters have since sought to prove or disprove the longest straight-line sea route, and the analogous route over land. Suggested but disproved longer routes include two nautical ones: from Norway to Antarctica – a valid route, but not in fact as long as the Pakistan to Kamchatka one; and from Québec to British Columbia, which turns out not to be a perfectly straight line.

One suggested longer overland route leads from from Wenling in China to Greenville in Liberia. But this line crosses the Dead Sea and if, as the authors say, that qualifies as a 'major body of water', it disqualifies the route as being entirely over land.

European leg

Image: Google Earth

Strangely enough, the direction from Portugal to China is due northeast

So Messrs. Chabukswar and Mukherjee decided to put the issue through a scientific wrangler. Instead of conducting an exhaustive search of all possible routes – more than 233 million great circles (3), as the authors suggest - they calculated the two paths using a so-called branch-and-bound algorithm.

They found that the original poster on Reddit was right: the longest sailable straight-line path does connect Pakistan to Kamchatka. To be precise, it links Sonmiani (25°17′ N, 66°40′ E), a coastal town (4) approximately 90 miles (145 km) northwest of Karachi, with an unnamed location in the Karaginsky District (58°37′ N, 162°14′ E), a virtually uninhabited part in the north of the Kamchatka peninsula. The path is almost 20,000 miles long (to be precise: 19,939.8 miles, or 32,090 km).

Asian leg

Image: Google Earth

Steppe by steppe...

The same algorithm was let loose on the dry-land variety of the straight-line question. Here, the answer links a point near Sagres (37°2′ N 8°55′ W) to a point in the south of the greater Quanzhou metro area (24◦33′ N, 118◦38′ E). The distance covered is much smaller than the longest straight line at sea: just short of 7,000 miles (6,984.8 miles, or 11,241 km).

The researchers formulate a few theoretical caveats to their result, and one practical one: "The problem was approached as a purely mathematical exercise. The authors do not recommend sailing or driving along the found paths".


There is hope, however, for whoever had their heart set on long straight-line travels. Here are a few of the world's longest straight-line roads (5):

1. Highway 10 (Saudi Arabia): 159 miles (256 km)

There is little remarkable about either Haradh or Al Batha, two dusty towns in Saudi Arabia's Rub-al-Khali desert, or the featureless distance between them. Except that almost that entire stretch is traversed by a dead-straight road. Leaving the oil town of Haradh in the interior of the country, Saudi Highway 10 heads due east in a curveless line for 159 miles (256 km), bending slightly before entering Al Batha, near the Gulf coast and the Saudi border with the United Arab Emirates. That makes Highway 10 the longest straight stretch of road in the world.

2. US-54 (United States): 108 miles (173 km)

In its entirety, US Route 54 runs from Griggsville, Illinois to El Paso, Texas, covering 1,197 miles (2,115 km). For 108 miles, from Liberal, Kansas to Dalhart, Texas, US-54 runs in a virtually straight line (passing through Oklahoma as well). There are a few slight kinks in over the course of 54's 'straight' trajectory, though.

3. Eyre Highway, Australia (90 miles, 145.6 km)

The entire Eyre Highway is 1,030 miles (1,660 km) long, linking Norseman in Western Australia to Port Augusta in South Australia across the deserted Nullarbor Plain. It is part of Highway 1 that connects Perth to Adelaide, and the only 'sealed' road between both states. Between Balladonia and Caiguna, the road is completely straight for 90 miles – the longest stretch of straight road in Australia, commonly known as '90 Mile Straight'.



Longest Straight Line Paths on Water or Land on the Earth, the paper by Rohan Chabukswar and Kushal Mukherjee, can be accessed here at arxiv.org.

Strange Maps #954

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(1) A 7,500-mile (12,000-km) China Railway cargo service from Yiwu, calling on Hamburg, London and Madrid. The service could become part of China's wider Belt and Road Initiative: a massive infrastructure project connecting Chinese manufacturing to its markets in Europe and elsewhere.

(2) Perhaps the 1,000-odd inhabitants of Sagres, the westernmost point on the European road network, will be less surprised. Sagres also is a terminus of the longest (non-straight) driveable distance between two points on earth. The other one is Khasan, a Russian city on the North Korean border, and the eastern terminus of that country's road network. The route connecting both places is 8,726 miles (14,043 km) long.

(3) A great circle or orthodrome is the largest circle that can be drawn on a spherical object.

(4) Sonmiani is also notable as the northernmost point of the Arabian Sea, a seaside resort for Karachiites and a launch site for the Pakistani space agency.

(5) Most so-called straight roads have slight curves, hence the many differing lists.

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Can dirt help us fight off stress? Groundbreaking new research shows how.

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Are modern societies trying too hard to be clean, at the detriment to public health? Scientists discovered that a microorganism living in dirt can actually be good for us, potentially helping the body to fight off stress. Harnessing its powers can lead to a "stress vaccine".

Researchers at the University of Colorado Boulder found that the fatty 10(Z)-hexadecenoic acid from the soil-residing bacterium Mycobacterium vaccae aids immune cells in blocking pathways that increase inflammation and the ability to combat stress.

The study's senior author and Integrative Physiology Professor Christopher Lowry described this fat as "one of the main ingredients" in the "special sauce" that causes the beneficial effects of the bacterium.

The finding goes hand in hand with the "hygiene hypothesis," initially proposed in 1989 by the British scientist David Strachan. He maintained that our generally sterile modern world prevents children from being exposed to certain microorganisms, resulting in compromised immune systems and greater incidences of asthma and allergies.

Contemporary research fine-tuned the hypothesis, finding that not interacting with so-called "old friends" or helpful microbes in the soil and the environment, rather than the ones that cause illnesses, is what's detrimental. In particular, our mental health could be at stake.

"The idea is that as humans have moved away from farms and an agricultural or hunter-gatherer existence into cities, we have lost contact with organisms that served to regulate our immune system and suppress inappropriate inflammation," explained Lowry. "That has put us at higher risk for inflammatory disease and stress-related psychiatric disorders."

University of Colorado Boulder

Christopher Lowry

This is not the first study on the subject from Lowry, who published previous work showing the connection between being exposed to healthy bacteria and mental health. He found that being raised with animals and dust in a rural environment helps children develop more stress-proof immune systems. Such kids were also likely to be less at risk for mental illnesses than people living in the city without pets.

Lowry's other work also pointed out that the soil-based bacterium Mycobacterium vaccae acts like an antidepressant when injected into rodents. It alters their behavior and has lasting anti-inflammatory effects on the brain, according to the press release from the University of Colorado Boulder. Prolonged inflammation can lead to such stress-related disorders as PTSD.

The new study from Lowry and his team identified why that worked by pinpointing the specific fatty acid responsible. They showed that when the 10(Z)-hexadecenoic acid gets into cells, it works like a lock, attaching itself to the peroxisome proliferator-activated receptor (PPAR). This allows it to block a number of key pathways responsible for inflammation. Pre-treating the cells with the acid (or lipid) made them withstand inflammation better.

Lowry thinks this understanding can lead to creating a "stress vaccine" that can be given to people in high-stress jobs, like first responders or soldiers. The vaccine can prevent the psychological effects of stress.

What's more, this friendly bacterium is not the only potentially helpful organism we can find in soil.

"This is just one strain of one species of one type of bacterium that is found in the soil but there are millions of other strains in soils," said Lowry. "We are just beginning to see the tip of the iceberg in terms of identifying the mechanisms through which they have evolved to keep us healthy. It should inspire awe in all of us."

Check out the study published in the journal Psychopharmacology.

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