The Mercator projection is a conformal cylindrical map projection that represents the three-dimensional Earth on a flat, two-dimensional surface. It was first presented by the Flemish geographer and cartographer Gerardus Mercator in 1569. The projection was created to solve the critical problem of marine navigation during the Age of Exploration. Its key innovation was representing a course of constant compass bearing, known as a rhumb line or loxodrome, as a straight line on the map. This property made it the standard map for sailors, allowing them to plot a straight-line course with a constant true bearing.
The mechanism of the Mercator projection involves mathematically projecting the globe onto a cylinder that touches the Earth at the equator. In this projection, the meridians of longitude are equally spaced parallel vertical lines, and the parallels of latitude are parallel horizontal straight lines. To maintain local angles and shapes (conformal property), the distance between the parallels of latitude increases exponentially as they move away from the equator toward the poles. This stretching causes a significant distortion of area, which is minimal near the equator but becomes extreme toward the poles. For example, on a Mercator map, Greenland appears larger than South America, even though Greenland is actually smaller than the Arabian Peninsula. Africa, which is about 14 times larger than Greenland, appears to be a similar size on the Mercator map.
The Mercator projection connects to the broader concept of map projections, which all introduce some form of distortion in area, shape, direction, or distance when translating a sphere to a plane. Its historical dominance has led to criticism, with alternatives like the Gall-Peters projection (1973) and the Equal Earth projection (2018) being promoted to show the true relative sizes of landmasses. In a recent change, the United Nations General Assembly resolved in September 2026 to promote equal-area map projections, specifically the Equal Earth projection, with 164 countries voting in favor, urging member states to use it in place of the traditional Mercator projection. Despite this, a variant called Web Mercator remains the de facto standard for online mapping services.