The Mercator projection is not a product of European chauvinism (African Union joins calls to end use of Mercator map that shrinks continent’s size, 15 August). All map projections are compromises geared to a particular use, as a direct transference of a sphere on to a flat surface is mathematically impossible. The Mercator projection was a brilliant solution to a critical need of 16th-century pilots: a map on which they could plot a straight line that would be a “straight” line on the Earth.
A mathematical marvel first put to paper by Gerard Mercator in 1569, it was not until 30 years later that the English mathematician Edward Wright sufficiently solved the complexities to make it practical. The Equal Earth map promoted by the African Union, like all others, simply makes different compromises for a different purpose. The African Union could well argue that the venerable Mercator projection is not the ideal choice for everyday use, but the notion that it marginalises Africa is a pointless distraction from real issues. European civilisation is guilty of centuries of crimes against the global south, but the Mercator projection is not one of them.
Thomas Suárez
London
• Your article doesn’t acknowledge that the surface of a sphere cannot be represented on a plane without distortion. This was proved mathematically by Carl Friedrich Gauss in the early 1800s. A raft of algorithms must be chosen from to translate what we see on the surface of the Earth into a two-dimensional map. This process is known as projection, and there are numerous techniques; each affects how a map ultimately looks. Every projection comes with trade-offs in shape, distance, direction, and land area.
The 16th-century Mercator projection preserves the shape of land masses (which is why it is so commonly used in schools) as well as direction (which is why it is used by navigators and Google Maps). What the Mercator projection sacrifices, however, is size representation, which is most distorted at the poles – meaning Africa is rendered smaller than it really is.
The Gall-Peters projection, meanwhile, nigh-on perfectly preserves land size, but heavily distorts shape. With the dawn of satellites and GPS, the Mercator projection has fallen from favour because it is no longer needed to aid navigation. Modern cartographers are free to blend equal-area maps, such as the Gall-Peters, with shape-preserving projections, such as the Mercator – and split a difference between size and shape. But there is no “correct” map projection, and the idea that the Mercator projection is symptomatic of European imperialism is a modern critique. The fairest way to see the Earth is to study a globe.
Hamish Monk
Chelmsford, Essex
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