Gerardus Mercator, a Flemish geographer and cartographer, introduced his namesake map projection in 1569. Developed specifically to assist marine navigation during the 16th century, the projection translated the three-dimensional globe onto a two-dimensional plane. Mercator provided a revolutionary system for plotting a course at sea. However, this mathematical solution is now widely known for its significant geographical inaccuracies when viewed as a general world map.
Exaggeration of Landmass Size
The most prominent distortion of the Mercator projection is the inflation of area for landmasses located farther away from the equator. The scale is mathematically true only along the equator itself. As one moves toward the poles, the size of countries and continents is increasingly exaggerated, creating an inaccurate visual representation of the world’s true proportions.
On a Mercator map, for instance, Greenland appears roughly the same size as the entire continent of Africa. In reality, Africa is approximately 14 times larger than Greenland, illustrating the severity of the distortion at high latitudes. Similarly, Alaska often looks comparable in size to Brazil, yet Brazil’s land area is nearly five times greater than Alaska’s.
Area distortion increases as the latitude approaches 90 degrees. Consequently, continents like Antarctica appear as a massive, continuous horizontal bar stretching across the bottom of the map. A Mercator map can never fully display the poles because the stretching required to project them would become mathematically infinite. The resulting massive appearance of northern countries like Canada and Russia, relative to equatorial regions, has shaped an inaccurate perception of their true land area.
Preservation of Local Shape and Angle
The Mercator projection is a “conformal” projection. This means that while the overall size of features is skewed, the local shapes of small areas and the angles between any two intersecting lines are accurately maintained. This property ensures that the shape of a country is correctly rendered, even if its size is incorrect relative to other regions.
The preservation of angles made the map essential for marine navigation. A straight line drawn anywhere on a Mercator map represents a line of constant compass bearing, known as a rhumb line or loxodrome. Navigators could measure a constant angle relative to the lines of longitude to determine their course. This allowed ships to sail a straight path without needing continuous course corrections.
The Cylindrical Projection Mechanism
The distortions seen in the Mercator map are a consequence of the mechanism used to create it. The projection is conceptualized by wrapping a cylinder of paper around the globe, tangent to the equator, and then projecting the Earth’s features onto that cylinder. Once the cylinder is unrolled, the result is a rectangular map grid.
On a spherical globe, the lines of longitude (meridians) converge at the poles. To create the rectangular grid of the Mercator map, these meridians must be forced into parallel, straight lines. This action causes an east-west stretching that increases with distance from the equator.
To maintain the correct local shape and angle (the conformal property), this stretching must be balanced by a corresponding north-south stretching. Therefore, the distance between the lines of latitude (parallels) is stretched increasingly farther apart toward the poles. This expansion is the reason why landmasses in polar regions appear disproportionately large.