As a science website, it is easy to get caught up in the mysteries of collapsing civilizations and the fine structure constant, while people out there on the Internet are struggling with why flying against the planet’s rotation doesn’t decrease flight times, and what the “Muffin Man” nursery rhyme is actually about.
This week, it has come to our attention that some people are a little confused as to why planes appear to take curved paths to their destinations, rather than straight paths. It’s a question that comes up surprisingly often on the Internet.
For anybody confused by this, first know that flight operators try to minimize fuel costs as much as possible. They are not simply taking the scenic route.
The answer is that flights are taking roughly straight paths to their destinations, but it doesn’t look like that when you represent their path on a two-dimensional map.
Representing a 3D world on a 2D map is always going to end up with some issues and some compromises. No matter how accurate you try to make it, you will end up with stretched areas, squashed countries, or else parts of the map cut out altogether.
The map you are likely familiar with is one based on the Mercator projection, published by cartographer Gerardus Mercator in 1569. It’s a cylindrical map projection, in which you place the globe into a cylinder and then project each point of the map onto a corresponding point on the cylinder.
Meridians (imaginary vertical lines going through the Earth from the North to the South Pole) are mapped onto vertical lines equally spaced apart on the map, and circles of latitude (imaginary horizontal lines from east to west) are mapped onto equally spaced horizontal lines.
The Mercator projection is good for navigation because it represents courses of constant bearing as straight segments, meaning ships have to course correct for the curvature of the Earth less frequently. However, it also results in distortions of size and shape. In cylindrical maps – as is the case with the Mercator projection – areas around the equator remain roughly accurate, but the further you move from the equator, the more distorted and inflated landmasses become.
In short, straight lines that don’t follow one line of latitude or longitude on a globe do not necessarily appear as straight lines on a flat map. And so, though a plane’s path may look like it is curved on a map, be assured they are taking you on the quickest possible route.
