Map projections explained: why Greenland looks huge and which projection to use
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Every flat map of the world is wrong somewhere. The Earth is close to a sphere, and there is no way to flatten the surface of a sphere onto paper without stretching, squashing or tearing it. A map projection is simply a set of rules for how that distortion is handled, and each one makes a different trade-off.
Why distortion is unavoidable
Try peeling an orange and pressing the peel flat. It splits or crumples. A projection decides where those splits and stretches go. Cartographers usually talk about four properties a map might try to keep:
- Shape (conformal): small features keep their correct shape and angles are preserved.
- Area (equal-area): regions are shown at the right size relative to each other.
- Distance (equidistant): distances are correct from one point, or along certain lines.
- Direction (azimuthal): directions from a central point are correct.
No projection can keep both shape and area correct everywhere at once, so every world map is a compromise.
The Greenland problem
The most familiar world map is based on the Mercator projection, designed in the sixteenth century for sailors. Its great strength is that a line of constant compass bearing is a straight line on the map, which made it ideal for plotting a course at sea. To achieve that, it keeps angles correct but stretches everything more and more the further you move from the equator.
The result is that Greenland looks roughly the size of Africa, when Africa is in fact around fourteen times larger. Europe, Russia, Canada and Antarctica all look far bigger than they are, while countries near the equator look small. This is sometimes called the Greenland problem, and it has shaped many people's mental picture of the world.
Most online street maps use a close variant of Mercator. That is a sensible choice when you are zoomed in, because streets meet at the correct angles and shapes look right, but it is a poor guide to comparing the size of countries when you zoom out. Some web maps now switch to a globe view at small scales for exactly this reason.
Common projections and what they are good for
- Mercator: navigation and zoomed-in street maps. Avoid it for comparing country sizes.
- Equal Earth: an equal-area world map introduced in 2018 with a pleasant, rounded outline. Good for thematic maps where area matters, such as population or land use.
- Gall-Peters: another equal-area projection, famous for correcting the size of Africa and South America, though it noticeably stretches shapes near the equator.
- Robinson: a compromise that keeps neither shape nor area exactly but looks balanced overall. It has long been popular in atlases and classrooms.
- Winkel tripel: another compromise projection, widely used for general reference world maps because it keeps overall distortion low.
- Azimuthal equidistant: centred on one point, it shows correct distances and directions from that point. Useful for radio and flight distances from a single location.
- Transverse Mercator and UTM: used for many national and topographic grids, because over a narrow strip the distortion is tiny.
Which projection should you use?
- Comparing areas or mapping data by region: choose an equal-area projection such as Equal Earth. If you colour countries by a statistic, a map that inflates northern countries will mislead readers.
- A general wall map: a compromise projection such as Robinson or Winkel tripel looks natural and avoids extreme distortion.
- Local or city maps: almost any conformal projection works, because distortion over a small area is negligible. Your national mapping agency's grid is usually the best choice.
- Navigation and web maps: Mercator-style maps remain practical because shapes and angles are right where you are looking.
- Distances from one place: an azimuthal equidistant map centred on that place.
A quick way to see the distortion yourself
Several free websites let you drag a country's outline across a Mercator map and watch it grow or shrink as it moves north or south. Dragging the United Kingdom to the equator, or Brazil up to Scandinavia, is a memorable lesson in how much the familiar map stretches.
Which projection do you prefer for your own maps, and why? Share your favourite in the comments.