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Father of the navigator's favourite map

Mercator's map remains a vital aid to sailors and pilots. Brian Dicks on the man behind the most familiar projection of the world. December 5 is the 400th anniversary of the death of Gerhardus Kremer (1512-1594). He is better known to the world as the scientific cartographer who simplified global navigation with a revolutionary map projection which became a format of world maps still used today.

The problems of representing the Earth's spherical shape as a flat map had taxed the graphical and mathematic ingenuity of cartographers since ancient times. Maps were rightly seen as compromises, portraying one or more of the Earth's essential properties, yet unable to show accurately on the same plane surface the four essentials of true shape, area, distance and cardinal direction. Only globes were capable of some reality, but these miniature Earth models were costly to make, difficult to store and impractical to carry around. Even the largest had a very small scale and showed little detail.

Born of German parents at Rupelmonde near Antwerp, Kremer's contribution to cartography was the product of a mercantile age which, by the 16th century, had brought great prosperity to the trading cities of north-west Europe. The knowledge explosion occasioned by the Voyages of Discovery created demand for reliable world maps and navigation charts, and Kremer's studies of mathematics, astronomy and philosophy at the famous University of Leuven, east of Brussels, led to his successful career in land surveying, instrument making and map engraving.

Briefly he was cosmographer and cartographer to the Hapsburg emperor Charles V. Then in I552 he moved to Duisburg, the German trading city at the confluence of the rivers Ruhr and Rhine. Here he founded his influential school of cartography, producing globes and maps that challenged those of the Flemish and Dutch in their accuracy and decorative design.

Kremer's greatest honour came in 1595, the year after his death when more than 100 of his world maps were published in book form. On the title page was a representation of the mythical giant Atlas supporting a globes and since this time the word atlas has been used to describe all collections of maps.

Kremer's lasting fame rests with the innovative world map he presented in 1569. It was based on a method of "projecting" a graticule (a grid of latitude and longitude) on to an imaginary cylinder enveloping the globe and touching only along the line of the equator. This produced one of the first rectangular-style world maps, but for navigational purposes its most important property was the fact that any straight line joining points on the map were also lines of constant bearings. Though not necessarily the shortest routes between locations, a map able to indicate true compass directions was of such value to Europe's trading nations that Kremer gained the epithet Mercator, meaning "merchant".

Preserving constant bearings meant sacrificing other important geographical features, especially the true area-size of land masses. Compensating for the Earth's curvature, Mercator's lines of longitude, on a globe converging at the poles, were splayed out as parallel lines. Lines of latitude, longest at the equator but mere points at the poles, were also altered and made of equal length with the equator, the only line along which latitude distances were true. This east-west "stretching" was mathematically compensated by a north-south "stretching", which spaced latitudes further apart with their in-creasing distance from the equator.

Despite disadvantages, Mercator's view of the world is the most familiar of all map projections, and many regard it as the only "true" map. Some relate its popularity to the way it reinforces European and North American global presence by inflating their size at the expense of many Third World regions.

However, the projection remains a vital aid to sea and air navigation, and a computerised variation is used for mapping satellite images.

Brian Dicks is a senior lecturer in geography at King Alfred's College, Winchester; a geography adviser and author.

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