Why Are Great Circles the Shortest Flight Path?
Why do you fly over Greenland in an airplane flight?
Or why is it that when you see flight paths on a map they always take a curved route between 2 cities? It’s because planes travel along the true shortest route in a 3-dimensional space.
This route is called a geodesic or great circle route. They are common in navigation, sailing and aviation.
But geodesics can be confusing when you’re looking at a 2-dimensional map as they follow quite the odd flight path. Let’s dig into this concept a bit deeper.
Great Circle Explained
In a flight path from New York to Madrid, if I asked you which line is shorter, you’d say the straight one, right?
However, a straight line in a 2-dimensional map is not the same as a straight line on a 3-dimensional globe.
This is why flight paths take an arc route between an origin and a destination.
Now here’s how the same flight paths look like on a sphere. Remember that the straight line in the Mercator map above followed the 40° latitude line.
This paints quite the different story, doesn’t it? It’s deceiving to the human eye.
The takeaway is this:
A route that looks longer on the map is because of the distortion created with map projections like the Mercator projection. In navigation, pilots often use great circles (geodesic) as the shortest distance flight.