Amazing Places

# This Is the Longest Straight Line You Could Sail

Have you ever wondered how far you could go in a straight line before you'd have to get on a boat, plane, or jet-ski? What about the other way around — how far could you sail in a straight line before the land gets in your way? At some point in the past, a nameless Wikipedia contributor made an educated guess about what the longest sailing path could be, and now, a team of researchers has brought the hard numbers to determine whether they're right.

## The Longest Line

In 2013, a Reddit user going by u/kepleronlyknows posted a hypothesis on r/MapPorn: This line is the longest straight distance that you can travel in a boat without running aground. That redditor didn't discover the line; they just found it listed on Wikipedia and created a new depiction of it. Now, you might be thinking, "But that's not a straight line!" It is, but the shape of the Earth gets in the way. If you drew it on a globe, you'd see that it forms a belt around the planet, as if you rearranged the equator to stretch from Pakistan to Russia.

But it's one thing to eyeball the longest distance and it's another thing to figure it out for certain. So a few years after kepleronlyknows (AKA Georgia-based environmental law attorney Patrick Anderson) published his rendition of the line, a physicist from United Technologies Research Center Ireland named Rohan Chabukswar set out to discover if there was a longer, perfectly-straight sea voyage out there. He teamed up with engineer Kushal Mukherjee from IBM Research India to map every possible straight route and suss out the longest one.

Actually, that's what they initially set out to do, but when the brute-force method turned out to be way too much work, they settled on using the branch-and-bound method to make their findings. Instead of checking each possibility separately, a branch-and-bound algorithm examines entire subsets of answers at once, quickly discarding the ones that fail to meet the conditions of the search. They focused on great circles, which wrap around the thickest part of a sphere, like the equator does. Using a standard laptop and the branch-and-bound algorithm, they had their answer in just 10 minutes. Kepleronlyknows was vindicated.

## Making the Trip

Let's talk about what it would mean for you to actually attempt this voyage. The full distance you'd travel is 19,940 miles (32,090 kilometers) — about 4/5 of the entire circumference of the globe. And before you book your ticket to Pakistan, be warned that there is some risk that this path isn't completely land-free. Since Chabukswar and Mukherjee's data had a resolution of 1.1 miles (1.8 kilometers), they might have missed any tiny islands smaller than that.

Regardless, you're probably going to want to make land at some point during your extra-long voyage, even if it's not, strictly speaking, allowed. Fortunately, the path skirts a few worthwhile sights. That straight line passes right between Madagascar and mainland Africa, putting the tropical archipelagos (and coral-diving meccas) Mayotte and Comoros directly in your way. Next, you'll pass by Port Elizabeth at the southernmost tip of South Africa. The next time you'll be within spitting distance of land is when you pass by the Antarctic Peninsula, and then you'll thread the needle to pass Tierra del Fuego in Chile. And then you've got the entire Pacific Ocean ahead of you, which you've got to cross the long way to get to your ultimate destination: Karaginsky District in Siberia. Whew, after a trip like that, you need a vacation.