On ancient maps, India is usually portrayed as much smaller than it is nowadays. Sometimes it’s perhaps only half the size. Surely mariners of the time could judge distances, especially along a relatively even coastline. What is the reason for the discrepancy?
• The root cause of India’s varying size is that you can’t peel the surface off a sphere and lay it flat without distorting it. Imagine trying to do so with orange peel. You have to choose how to distort it: you can preserve area, distance or direction, but not all of them. This compromise is inherent in all map projections of Earth’s surface.
There is no perfect depiction, and choosing the appropriate one depends on the map’s purpose. The 16th-century Mercator projection preserves compass directions: the north-south and east-west lines are straight (although all other straight journeys look curved, as you may have seen on in-flight aircraft route maps). This preservation of compass direction, as well as the accurate depiction of coastal features, is what sailors cared about – and they were the most important customers for maps at the time. But the Mercator projection has a huge drawback. It makes a 40-kilometre circle around the North Pole as wide as the 40,000-kilometre equator. Africa looks smaller than Greenland when it is actually 14 times larger, and India looks tiny.
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So an 1855 alternative called the Gall projection was revived in 1973 as the Peters projection. This squashes the vertical distance near the poles to make up for the inherent horizontal expansion. The result is that northern countries (and Australia) are unrecognisable, but the relative area of each country is conserved. If you are prepared to give up on rectangular maps, a semi-oval is a good compromise, although things at the edges still suffer: the 1805 Mollweide map is a popular equal-area projection, and the National Geographic Society uses the 1921 Winkel Tripel projection.
Online maps such as Google Maps still use a simplified Mercator projection because preserving compass directions on a rectangle is their main purpose.
Ron Dippold, San Diego, California, US
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This article appeared in print under the headline “Map lag”
