The Mercator Map and Circles
How circles of increasing radius, centred on a city such as Paris, are distorted once drawn on a Mercator projection.
Where this idea comes from
Start here — this is the source that inspired this exploration.
Introduction
Social media posts claiming a map projection 'lies' are worth checking mathematically rather than taking on faith. On a Mercator map, a circle of fixed radius drawn on the globe no longer looks like a circle once it is centred somewhere other than the equator - it stretches into an oval, and the distortion grows with distance from the equator. This exploration asks you to draw circles of increasing radius centred on a city of your choice, plot them on a Mercator projection, and use trigonometry to predict the distorted shape before you draw it.
Guiding Questions
- What does a circle of fixed radius on the globe look like when drawn on a Mercator map?
- Centre circles of increasing radius on a city of your choice. At what radius does the map shape stop looking like a circle?
- Can you use trigonometry to predict the distorted shape before plotting it?
- How would the same circles look on a different projection?