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Shortest flight path – great circle routes

Choosing the shortest flight route is important to save both time and fuel. Here you can learn all about how great circle navigation helps the aviation industry to optimize its paths and why the shortest routes are usually displayed as an arc in a map.

The fact that the Earth isn’t flat was settled quite a few years ago, and the spherical shape of our planet is actually an important fact to consider when traveling by air. To find the shortest route on a sphere, you need to use the so-called great circles. A great circle is the largest possible circle that can be drawn on a sphere, and can be defined as any circle that divides the sphere into two equal halves and is centered on the sphere's center.

As confusing as this may sound, a great circle is actually the shortest path between any two points on the surface of a sphere. For example on Earth, the equator is a great circle, as are the lines of longitude that pass through both the North and South Poles.

When it comes to long distance flights around the world, the routes are generally created based on the great circles. Traveling along a great circle means that you might not travel along a straight line on a flat map. Take a look at the images below to see the difference in the route between London and Los Angeles when presented on a sphere and on a flat map. Note that the lines pass the same geographical points on the route – for example the south of Greenland.

great circle route london los angeles
When displayed on a sphere, it is easy to tell that this is the shortest route between London and Los Angeles. 
great circle routes shortest flight path
On the other hand, on a two-dimensional map the shortest flight path following a great circle will appear as an arc instead of as a straight line. This is because the southern and northern hemispheres are stretched out on the flat map.

The appearance of a great circle route on a flat map also depends on its proximity to the equator – routes passing close to the equator will appear as a straight line while routes further away will appear as much more of an arc. Below you find one example of each kind of route.

great circle routes close to equator
The route between Addis Ababa and Singapore matches a great circle close to the equator, making it appear as a straight line on a flat map.
great circle route north pole los angeles dubai
An extreme example of a great circle route far from the equator is the one connecting the airports in Los Angeles and Dubai. This route actually finds its closest path on a great circle passing north of Greenland – and yes, this is the shortest route between the two cities.
great circle route los angeles dubai
The same route between Los Angeles and Dubai, but displayed on a sphere.

But why is a great circle route the shortest option? The easiest way to explain it without going deep into mathematics is probably to state the fact that a straight line in a two-dimensional map is not the same as a straight line on a three-dimensional globe. This means that choosing a great circle route instead of flying in, what appears to be, a straight line saves both time and fuel.

Popular great circle routes

Great circles are mainly being used when it comes to long distance flights, for example when traveling from the US to Europe or Asia. Listed below you find some examples of great circle routes.

  • New York (JFK) to Tokyo (HND) – This route crosses over the North Pacific Ocean, offering the shortest path between these major cities on opposite sides of the globe.

  • London (LHR) to Los Angeles (LAX) – Flights on this route usually pass over Greenland and Canada, reflecting the curvature of the Earth and shortening the travel distance.

  • Sydney (SYD) to Santiago (SCL) – This is one of the longest direct flights in the world, and it generally takes a route over the South Pacific Ocean, closely following a great circle.

  • Johannesburg (JNB) to New York (JFK) – This flight typically crosses over the Atlantic Ocean, near the equator, optimizing the distance traveled between the southern tip of Africa and the eastern coast of the US.

  • San Francisco (SFO) to Hong Kong (HKG) – The route crosses the Pacific Ocean, taking advantage of the Earth’s curvature to minimize the flight distance.

  • Helsinki (HEL) to Bangkok (BKK) – Flights on this route often pass over parts of Russia, China and other countries in Central Asia. This north-to-south trajectory takes advantage of the great circle route to reduce the distance traveled between Finland and Thailand.

There are different ways to project the earth globe on a flat map and the most common used on the web including Google Maps and the maps we use on is the Web Mercator Projection