Map projections and distortion

Earth is a sphere, but maps are flat. Whenever cartographers take the curved surface of the globe and stretch it onto a piece of paper, they have to make choices — and every choice creates some kind of distortion. A flat map can preserve shapes, OR sizes, OR distances, OR directions — but it can never preserve all of these at the same time. The mathematical method used to flatten Earth is called a map projection.

The Mercator projection

The Mercator projection was invented in 1569 by Gerardus Mercator for sailors. Its great strength is that it preserves angles and shapes locally — a straight line on a Mercator map is a line of constant compass bearing, which made it perfect for navigation. Its weakness is that it dramatically distorts size near the poles. Greenland looks as big as Africa on a Mercator map, but Africa is actually about 14 times larger. Antarctica appears as a giant ribbon across the bottom.

The Robinson projection

Arthur Robinson designed his projection in 1963 as a compromise. It does not perfectly preserve area, shape, distance, or direction, but it distorts each one only a little. The result looks pleasant and balanced, and from 1988 to 1998 the National Geographic Society used Robinson as its standard world map. Many modern classroom atlases still use it because the continents look "about right" without any single feature being badly warped.

The Peters projection (equal-area)

The Peters projection is an equal-area projection. That means every country is shown at its correct relative size — Africa looks correctly enormous, Europe looks correctly small, and Greenland shrinks to its real size. Shapes are stretched and look tall and thin near the equator, but no continent is "made bigger" than it should be. Schools and aid organizations sometimes prefer Peters because it gives a more honest picture of how much of Earth's land lies in the tropics and the southern hemisphere.

Goode's Homolosine projection

Goode's Homolosine is an interrupted projection. Instead of one continuous rectangle, the map is split open along the oceans so that the continents can be shown with very little size or shape distortion. The trade-off is obvious: the oceans are sliced into pieces, so the map is useless for plotting an ocean voyage. Goode's is excellent for showing the continents accurately and is often used in atlases for population, climate, or biome maps where landmass is the important thing.

The fundamental tradeoff

There is no "best" projection — only a projection that is best for a particular job. A sailor crossing an ocean wants Mercator. An aid worker counting people in the tropics wants Peters or Goode's. A family that wants a balanced wall poster wants Robinson. A globe — a small, three-dimensional Earth — is the only model that has no distortion at all, but globes are bulky and you cannot fold one into a textbook. Every flat map is a compromise; the cartographer's job is to pick the compromise that best suits the map's purpose.

• Mercator — preserves angles and shapes locally; distorts size near the poles; great for navigation.
• Robinson — gentle compromise; no property perfectly preserved; popular for classroom world maps.
• Peters — equal-area; every country at correct relative size; shapes look stretched.
• Goode's Homolosine — interrupted; continents very accurate; oceans split apart.
• Globe — three-dimensional; no distortion at all; impractical for a notebook.