Gerardus Mercator, original name Gerard De Cremer, or Kremer?, (born March 5, 1512, Rupelmonde, Flanders [now in Belgium]—died December 2, 1594, Duisburg, Duchy of Cleve [Germany]), Flemish cartographer whose most important innovation was a map, embodying what was later known as the Mercator projection, on which parallels and meridians are rendered as straight lines spaced so as to produce at any point an accurate ratio of latitude to longitude. He also introduced the term atlas for a collection of maps.

Mercator’s family had moved from Germany to Flanders shortly before he was born. He was educated in Hertogenbosch (Netherlands), receiving training in Christian doctrine, dialectics, and Latin. In 1530 he entered the Catholic University of Leuven (Louvain [Belgium]) to study the humanities and philosophy and graduated with a master’s degree in 1532.

Religious doubts assailed him about this time, for he could not reconcile the biblical account of the origin of the universe with that of Aristotle. After two years of study which led him to Antwerp and Mechelen he emerged from his personal crisis, fortified in his faith, with less enthusiasm for philosophical speculation. Moreover, he brought back to Leuven a freshly acquired taste for geography.

Under the guidance of Gemma Frisius, the leading theoretical mathematician in the Low Countries, who was also a physician and astronomer, Mercator mastered the essentials of mathematics, geography, and astronomy. Frisius and Mercator also frequented the workshop of Gaspar à Myrica, an engraver and goldsmith. The combined work of these three men soon made Leuven an important centre for the construction of globes, maps, and astronomical instruments. In 1534 Mercator married Barbara Schellekens, by whom he had six children.

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By the time he was age 24, Mercator was a superb engraver, an outstanding calligrapher, and a highly skilled scientific-instrument maker. In 1535–36 he cooperated with Myrica and Frisius in constructing a terrestrial globe and in 1537 its celestial counterpart. These globes demonstrate the free and graceful italic lettering with which Mercator was to change the face of 16th-century maps. During that period he also began to build his reputation as the foremost geographer of the century with a series of printed cartographic works: in 1537 a map of Palestine, in 1538 a map of the world on a double heart-shaped projection, and about 1540 a map of Flanders. In 1540 he also published a concise manual on italic lettering, the Literarum Latinarum quas Italicas cursoriasque vocant scribende ratio, for which he engraved the wood blocks himself.

In 1544 he was arrested and imprisoned on a charge of heresy. His inclination to Protestantism, and frequent absences from Leuven to gather information for his maps, had aroused suspicions; he was one of 43 citizens so charged. But the university authorities stood behind him. He was released after seven months and resumed his former way of life. He obtained a privilege to print and publish books and was free to continue his scientific studies.

In 1552 Mercator moved permanently to Duisburg in the Duchy of Cleve. Once there, he became a well-known figure. He assisted the duke in establishing a grammar school by helping to design its curriculum. After establishing a cartographic workshop and engaging his own engravers, he returned to his main interest.

In 1554 he published a map of Europe that he had begun at Leuven, and between 1559 and 1562 he taught mathematics in the grammar school. During these busy years he also undertook genealogical research for Duke Wilhelm, drew up a Concordance of the Gospels, and composed a detailed commentary on the first part of the Letter of Paul to the Romans. In 1564 he completed a map of Lorraine (now lost) and another of the British Isles. Public recognition of his accomplishments came in 1564 with his appointment as court “cosmographer” to Duke Wilhelm of Cleve. During these years he perfected his projection, which enabled mariners to steer a course over long distances by plotting straight lines without continual adjustment of compass readings. This technique immortalized his name in the “Mercator projection,” which he used on his map of the world in 1569.

(Left) Globe of the Earth with no land distortion and (right) the Mercator projection with increased land distortion, especially in the 60° to 90° latitudes Encyclopædia Britannica, Inc.

Mercator then began to execute a series of publications intended to describe the creation of the world and its subsequent history. This Atlas—the term still used to indicate a collection of maps—was never fully realized.

In 1569, as the first section, he published a chronology of the world from the Creation to 1568. He then published 27 of the maps originally prepared by the Greek geographer Ptolemy, with corrections and commentary in 1578, under the title Tabulae Geographicae C. Ptolemei ad mentem autoris restitutae et emendatae. The next part of the Atlas, consisting of a set of new maps covering France, Germany, and the Netherlands, came out in 1585, with maps of Italy, “Sclavonia” (now the Balkan countries), and Greece following in 1589. A last section, on the British Isles, was included in an edition with the previous sections, which was seen through the press after his death by his son in 1595. Another printing followed in 1602, and further maps were added in a later edition of 1606, usually called the “Mercator–Hondius Atlas.”