Gerardus Mercator Simulacrum

The Life

Gerardus Mercator — born Gerard de Kremer — was born in Rupelmonde, in the Spanish Netherlands, in 1512. He studied at Louvain under the humanist Gemma Frisius and became a surveyor, instrument-maker, and engraver of maps. An accusation of Lutheran heresy led to his imprisonment for seven months in 1544, and after his release he moved to Duisburg in the Duchy of Cleves, where he spent the rest of his long working life. He died in 1594.

The Thought

Mercator's chief technical contribution was the projection that now bears his name, first applied to the world map he published in 1569. The problem he set himself was a specifically navigational one: on a flat map, a line of constant compass bearing — a *rhumb line*, the line a sailor follows by holding a fixed heading — should appear as a straight line, so that a navigator can draw a course with a ruler. No previous projection had this property. Mercator solved it by stretching the latitudes increasingly toward the poles, in a mathematical progression that Edward Wright in 1599 gave rigorous form but that Mercator himself had empirically approximated.

The cost of the solution is the extreme distortion of areas near the poles, which makes Greenland look the size of Africa. Mercator was aware of this; his 1569 map carries explanatory texts about the projection's purposes and limits. But for a navigator laying out a voyage, the distortion was a price worth paying; a compass course on a Mercator chart is a straight line, and a straight line is what a helmsman can steer.

Mercator also produced a monumental *Atlas* (the name itself is his coinage; earlier collections of maps had no general term) whose first edition appeared in the year of his death. The *Atlas* gathered regional maps into a systematic volume and established the form that Abraham Ortelius's earlier *Theatrum* had pioneered.

The Legacy

The Mercator projection was adopted almost universally as the standard projection for marine charts within fifty years of its invention, and has remained so for most practical navigational purposes ever since. Its world-map applications have been more contested — the projection's equatorial bias reinforces visual assumptions about the relative size of northern and southern countries — and modern presentation-level world maps increasingly use equal-area alternatives. But for navigation the projection is irreplaceable, and for four centuries it has been the image most people carry of the world's shape. Mercator's *Atlas* established the form of the modern geographical reference book.