Map Projections Explained: Why Every Map Lies
You cannot flatten a sphere without distortion. Learn what different projections preserve, and how to pick the right one.
A map projection is a systematic way of turning the latitudes and longitudes of locations on the curved Earth into positions on a flat plane. Because the Earth is curved, every projection distorts something: shape, area, distance, or direction. There is no perfect projection — only trade-offs. This guide explains why distortion is unavoidable, what the major projection families preserve, and how to choose the right one for your map.
Why distortion is unavoidable
In 1828, Carl Friedrich Gauss proved his Theorema Egregium ('remarkable theorem'), which implies that a sphere's surface cannot be flattened without distortion — the sphere has intrinsic curvature that a plane lacks. Intuitively: try flattening an orange peel and it tears or stretches. Every flat map of the Earth is therefore a compromise, and the entire art of map projections is choosing which distortion to accept. A projection can preserve some properties perfectly, but never all of them at once. Understanding which property a projection preserves — and which it sacrifices — is the key to reading maps critically and choosing projections honestly.
The four properties a projection can preserve
Cartographers talk about four properties. Conformal projections preserve local shapes and angles — a small circle on the globe stays a small circle on the map (though it may change size). Equal-area projections preserve area proportions, so a country twice as large on the globe looks twice as large on the map. Equidistant projections preserve distances from one or two special points (never everywhere). Compromise projections preserve nothing exactly but keep all distortions moderate, which is why they are popular for general world maps. No projection is conformal and equal-area at once — that combination is mathematically impossible, so every choice is a trade-off you should make deliberately.
Cylindrical projections
Imagine wrapping a cylinder around the globe and projecting the surface onto it, then unrolling the cylinder. The Mercator projection (1569) is the famous example: it is conformal, so compass bearings plot as straight lines — invaluable for marine navigation for centuries. But it hugely exaggerates areas near the poles: Greenland looks as big as Africa, when Africa is actually about 14 times larger. Equal-area cylindrical projections like Gall-Peters fix the area distortion but stretch shapes vertically near the equator and squash them near the poles. The Miller cylindrical is a compromise used for world maps. Cylindrical projections are natural for world maps and navigation, poor for showing true relative sizes.
Conic projections
Project the globe onto a cone placed over it, then unroll the cone. Conic projections excel at mid-latitude regions with wide east-west extent — exactly the shape of countries like the USA, Russia or China. The Lambert conformal conic preserves shapes locally and is the standard for aeronautical charts and many national mapping systems in mid-latitudes. The Albers equal-area conic preserves area and is the go-to for thematic maps of continents (showing population, election results, or climate data) where correct relative size matters. Because the cone touches the globe along one or two standard parallels, distortion is minimal near those latitudes and grows away from them.
Azimuthal projections
Project the globe from a point onto a flat plane touching it — like photographing the Earth from space. Azimuthal projections are centred on one point and are the natural choice for maps centred on the poles, for radio propagation maps, and for showing true directions from the centre. The stereographic projection is conformal and widely used for polar regions. The Lambert azimuthal equal-area preserves area and is used for whole-hemisphere thematic maps. The azimuthal equidistant projection preserves true distance and direction from the centre point — it is the projection behind the familiar UN flag emblem, centred on the North Pole.
Pseudocylindrical and compromise projections
Pseudocylindrical projections keep parallels as straight lines but curve the meridians, which tames the polar exaggeration of true cylindricals. The Robinson projection, long used by National Geographic, and the Winkel Tripel (German for 'triple', minimising three kinds of distortion), now National Geographic's standard, are compromise projections: they preserve nothing exactly but look balanced and familiar for world reference maps. The Mollweide is an equal-area pseudocylindrical popular for global data visualisation. If you need a world map for a general audience and no single property dominates, a compromise projection is usually the honest choice.
Web Mercator: the projection that rules online maps
Web Mercator (EPSG:3857) is the projection behind Google Maps, OpenStreetMap and nearly every tiled web map. It is a variant of the Mercator optimised for fast computation and seamless square tiles at every zoom level. Its conformal property keeps local shapes correct, which is why streets look right when you zoom into a city. But it inherits Mercator's area distortion — severe near the poles, which is why Greenland and Antarctica look enormous on web maps — and it cannot show the poles at all (it cuts off around ±85°). For interactive street maps it is the pragmatic standard; for any analysis involving area or global comparison, reproject your data first.
Tissot's indicatrix: seeing distortion
Nineteenth-century cartographer Nicolas Tissot invented an elegant way to visualise what a projection does: draw identical small circles on the globe and see what they become on the map. Where the projection is conformal, they stay circles (changing only size); where it distorts, they become ellipses whose stretch shows the direction and amount of distortion. Many projection references show Tissot's indicatrix grids, and learning to read them is the fastest way to develop intuition: a glance tells you whether a projection stretches the poles, shears the mid-latitudes, or stays faithful in a particular region.
How to pick a projection
Ask what matters most for your map's purpose, then choose honestly. Navigation and local shape: conformal (Mercator for marine, Lambert conformal conic for aviation charts, stereographic for polar). Thematic data where relative size matters (population density, election maps): equal-area (Albers for continents, Mollweide or Equal Earth for world). Distances from one point (radio range, flight range): azimuthal equidistant centred on that point. General world reference: compromise (Winkel Tripel, Robinson, Natural Earth). And match the projection to the region: conic for wide mid-latitude countries, transverse Mercator (like UTM) for tall narrow regions, azimuthal for polar areas. State the projection in your map's metadata — a map without a stated projection is hiding its distortions.
Go deeper
Keep reading: how the UTM grid flattens the Earth, our guide to how map scale works, or experiment hands-on with the coordinate converter tool.
Frequently asked questions
What is the most accurate map projection?
No projection is universally accurate — each preserves some properties and distorts others. The honest answer is always 'accurate for what?' Choose based on whether shape, area, distance or direction matters most for your map.
Why does Greenland look huge on Mercator maps?
Mercator is conformal, and the price of preserving local shape is stretching area increasingly toward the poles. Greenland looks similar in size to Africa on a Mercator map, but Africa is actually about 14 times larger.
What projection should I use for measuring distances?
Use an equidistant projection centred on your region, or better, compute distances directly on the sphere or ellipsoid with the Haversine or Vincenty formula. Never measure distances on a Web Mercator world map.
Why do online maps all use Web Mercator?
It tiles neatly into squares at every zoom level, computes fast, and keeps local shapes correct for street navigation. The trade-off — severe area distortion near the poles — is acceptable for its purpose but makes it wrong for global comparisons.
Sources & data
Authoritative references used to research and verify this article: