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Why Flights Look Curved on a Map (And How to Plot It in Python)
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Have you ever looked at the flight map on a long-haul flight and wondered why your plane seems to be heading north instead of flying straight to its destination?
On a map, a flight from New York to London can look like a huge detour. It’s tempting to think the plane would get there faster by following a straight line. But it’s already taking the shortest route. The catch is that we’re looking at a spherical planet on a flat map, and that changes how the route appears.
In this post, we’ll see why maps can be misleading. With a few lines of Python in Google Colab — and no external datasets — we’ll calculate and plot flight paths to see what the shortest route actually looks like.
Great Circles and Rhumb Lines
Before we start coding, it helps to know about two kinds of routes.
A rhumb line is a route that keeps the same compass heading throughout the journey. On a Mercator map, it appears as a straight line. But on a spherical Earth, it’s usually longer than the shortest possible route.
That shortest route is called a great-circle route. It follows the curve of the Earth, so its direction gradually changes along the way. On a flat map, it often appears as a wide arc — which can make it look like a detour, even though it’s the shorter path.
