Mercator Projection: Why Greenland Looks as Big as Africa

The Mercator projection is a way of drawing the round Earth on a flat rectangle so that every angle on the map matches the angle on the ground. Gerardus Mercator published it in 1569 for sailors: a course of constant compass bearing, called a rhumb line, appears as a straight line, so a navigator could lay a ruler between two ports and read off the heading to steer.

It is a cylindrical projection. Picture a cylinder wrapped around the Equator: meridians become evenly spaced vertical lines and parallels become horizontal lines. On a sphere of radius R, a point at longitude λ and latitude φ lands at:

• x = R × (λ − λ₀)
• y = R × ln(tan(45° + φ/2))

The first formula is simple. The second is the clever part: it spaces the parallels farther and farther apart toward the poles, by exactly the amount needed to keep shapes right. At 90° the value of y is infinite, so a Mercator map can never show the poles. Web maps cut it off at about 85.05° north and south.

Mercator is not "the wrong map". It does one job perfectly (true angles) and pays for it with area, which is the trade-off every flat map makes in some form. The overview of map projections compares it with the alternatives.

On a globe the meridians squeeze together toward the poles. At latitude φ, a degree of longitude is only cos φ as long as at the Equator: about 87% at 30°, half at 60°. Mercator draws the meridians parallel instead, so every parallel is stretched sideways by a factor of 1/cos φ, also written sec φ.

If the map stopped there, shapes would be squashed: wide but not tall. Mercator fixes that by stretching north-south by the same factor at every latitude. Because the stretch is equal in both directions at any given point, small circles stay circles and right angles stay right angles. That property is called conformal.

The figure shows this with Tissot's indicatrix: identical circles on the ground, each 4° of arc in radius, drawn on a Mercator map. They stay round, but their size grows with latitude.

The same stretch explains why a straight line on the map is a rhumb line. A rhumb line crosses every meridian at the same angle; since Mercator keeps angles and draws meridians as parallel vertical lines, a constant angle to vertical lines is a straight line. Navigators used that for centuries. Great circles, the true shortest routes, show up as curves bowing toward the pole.

The linear scale factor of the Mercator projection is k = sec φ = 1 / cos φ. Lengths in every direction are multiplied by k, so areas are multiplied by k² = sec² φ. These values are computed for a sphere; on the WGS84 ellipsoid the factor is smaller by at most 0.34%, which does not change any conclusion here.

Two consequences matter in practice. First, a country at 60° is drawn four times larger than an identical country on the Equator. Second, the scale bar on a Mercator map is only valid at one latitude. A bar that reads 100 miles at the Equator is 50 miles long on the ground at 60°.

No. Greenland covers 2,166,086 km² (836,330 sq mi) according to Statistics Greenland. Africa covers about 30.3 million km² (11.7 million sq mi) in the UN Demographic Yearbook. Africa is roughly 14 times larger than Greenland.

They look similar because Greenland sits between about 60° and 84° north, where Mercator inflates area 4 to 80 times, while Africa straddles the Equator, where the stretch is small. Measured on the Natural Earth 1:50m outlines we use for maps on this site, the result is striking:

• Greenland is drawn at about 16.4 times its true area on a Mercator map.
• Africa is drawn at about 1.12 times its true area.
• In equator-scale map units, Greenland occupies about 35 million km² of paper and Africa about 33 million, so Greenland actually draws slightly larger.

A better mental comparison: Greenland is a little smaller than the Democratic Republic of the Congo (about 2.15 million versus 2.33 million km² in the same outlines). The Greenland vs Africa comparison overlays both at true scale, and the country size comparison tool lets you drag any country to a new latitude and watch its true size.

Greenland is the famous example, but every high-latitude place is inflated. Here is how Mercator scales several countries, computed from the same outlines (true area on an equal-area sphere, then the area each shape occupies on a Mercator map):

On a Mercator map, Russia looks more than twice the size of Africa, yet Africa is about 1.8 times larger. Canada appears larger than Africa while being about a third of its area. Alaska looks comparable to the whole contiguous United States. Antarctica, smaller than South America, becomes an endless white band along the bottom edge.

These numbers come from generalized 1:50m outlines, so they differ from official land areas by a percent or two; the distortion factors are what matter.

Google Maps, OpenStreetMap and most web map libraries (including the MapLibre maps on this site) use a variant called Web Mercator, registered as EPSG:3857 "WGS 84 / Pseudo-Mercator". It takes WGS84 latitude and longitude and plugs them into the spherical Mercator formulas, as if the ellipsoid were a sphere. The EPSG registry flags it as not a recognized geodetic system and notes scale differences of about 0.7% from true ellipsoidal Mercator.

Why web maps chose it:

1. Square tiles. Cutting the map at ±85.05113° (the latitude where y equals x at 180°) makes the whole world a square, which splits cleanly into 256-pixel tiles at every zoom level.
2. Local shapes stay right. Because it is conformal to within a fraction of a percent, street corners stay square and buildings keep their shape at street zoom, where nobody notices the area distortion.
3. North is always up. Meridians are vertical everywhere, which keeps panning simple.

The cost is the same as on paper. At world zoom, Greenland, Canada and Scandinavia are inflated. A circle with a fixed ground radius also grows on screen toward the poles: a 100-mile circle drawn with the map radius tool near Oslo is twice as wide on screen as the same circle near the Equator, even though both enclose the same ground area. Our tools compute distances and areas on the WGS84 ellipsoid, not from screen pixels, so the numbers stay correct even when the drawing looks stretched.

A straight line on a Mercator map is a rhumb line: a constant compass heading. It is easy to steer but it is not the shortest path. The shortest path between two points on the Earth is a geodesic (on a sphere, a great circle), and on Mercator it bends toward the nearer pole.

The gap grows with distance and latitude. Computed for real routes (geodesic on the WGS84 ellipsoid, rhumb line on a mean-radius sphere):

That is why transpacific flights arc up toward Alaska on a flat map: they are flying the straight route on the globe. The distance between cities calculator draws the geodesic route, which looks curved on its Mercator base map for the same reason.

Mercator is the right choice when angles matter more than areas:

• Marine and some aeronautical navigation charts, where a rhumb line course is plotted with a ruler and protractor.
• Street-level web maps, where an area of a few miles has essentially no distortion and conformality keeps shapes familiar.
• Narrow east-west strips near the Equator, where the scale factor stays close to 1.
• Its transverse form, which wraps the cylinder along a meridian instead of the Equator. Transverse Mercator underlies the UTM grid and many state plane zones, giving accurate local maps in narrow north-south strips.

Avoid it for:

• World maps that compare sizes: population, land use, election results, climate data. Use an equal-area projection such as Equal Earth or Mollweide.
• Classroom wall maps, where the Greenland effect shapes how people picture the world.
• Measuring distance with a ruler across large areas. The scale changes with latitude, so a ruler measurement can be off by a factor of two or more.

Our own printable world maps in the blank map library use Equal Earth for exactly this reason, while the interactive maps use Web Mercator so they can zoom to street level.