Eli5: Why do some flights go so far north before crossing the Pacific Ocean?


There is a flight going from Dallas Texas to Tokyo but they appear to be going all the way to Alaska before crossing and coming back down.

In: 1

Because that is closer to the most direct route between those two points. You are looking at a flat map, but this is just a projection of a mostly spherical map. If you looked at an actual globe you’d see this–the projection skews your perceptions.


You’re probably looking or envisioning a Mercator projection maps. Which east-west circle has a greater circumference?

A) The equator

B) The circle halfway between the equator and the pole

Clearly the equator represents a longer path than the circle at 45 degrees latitude, and yet the map you are looking at represents them as the exact same length (the both go from edge to edge). This is why Greenland looks so much larger than it actually is (it’s stretched considerable in the east-west direction.

What this means is that two points the same distance apart in an east-west direction are actually closer together than they appear on your flat map, so although the line is longer on your flat map, the actual distance on a round globe will shorter.

>There is a flight going from Dallas Texas to Tokyo but they appear to be going all the way to Alaska before crossing and coming back down.

A direct flight from Dallas to Tokyo will graze Alaska. It’s a straight line, the shortest path. If whatever flight map or tool you happen to be checking right now doesn’t *show* it to be a straight line it’s because you’re seeing a map projection – an approximation that does not fully represent the non-Euclidian geometry you have to work with when traveling large distances on top of a globe. Projections always lose some sort of aspect of real world geometry in trying to portray a 3-dimensional surface in a 2D-plane.

In short: The map is incorrect because it *has* to be incorrect. The real-world path is a straight line.

They are actually following the smallest path between these two cities. Remember that the earth is a globe that gets distorted when you put it into a map.

So if you take a globe, put Dallas in front of you and your finger in Tokyo and trace an arc over the surface of the globe connecting these two cities, you will see that it goes very near Alaska.

The shortest path between to points on a sphere is called a great circle. You can use this tool to calculate the great circle between any two airports.


Because the Earth is a sphere. The term you’re looking for is called a “Great Circle”.

Imagine you took a sharpie and drew a black line from Texas to Tokyo, and then took a rubber band and wrapped it around the Earth connecting both Texas and Tokyo (it would be like a weird equator). Now measure the length of the lines, the rubber band distance is much shorter than the sharpie line distance. This only works a globe though because it’s 3D geometry, it wouldn’t work on a flat map.