Mapping the Earth: why every map is a compromise

The shape of the Earth

The Earth is not a perfect ball. Because it spins, it bulges a little around the Equator and is a bit flatter at the poles; this shape is called an oblate spheroid. Take an orange as a model of the Earth, peel it carefully and try to lay the peel flat. However you press it, it splits or wrinkles. A map has the same problem: it must show a curved surface on flat paper, so something always gets stretched or squeezed.

What is a map projection?

The way mapmakers transfer the curved Earth onto a flat sheet is known as a map projection. Mapmakers, called cartographers, have tried many projections over the centuries. Some keep the shapes of countries right but get their sizes wrong; others keep the sizes right but bend the shapes. No projection can keep everything correct at once, so every world map is a compromise. A map made for sailors, a map for comparing the areas of countries and a map for a school atlas may therefore all look slightly different, even though they show the same Earth.

Mercator and Robinson

The Mercator projection keeps shapes and directions correct. A straight line on it is a steady compass bearing, which is why it has long helped sailors navigate. The price is size: lands look bigger and bigger towards the poles, so Greenland looks as big as Africa and larger than India, though India is in fact about one and a half times its area. The Robinson projection accepts small errors in both size and shape so that nothing is badly distorted, which gives a more realistic-looking map of the whole world. To understand the world fairly, it helps to look at more than one projection, not just one.

Reading a physical map

This chapter uses physical maps, which show the land and water rather than countries. They have their own colour language. Blue marks water bodies such as oceans, seas, lakes and rivers. Green shows plains, yellow or brown shows plateaus, and dark brown shows high mountains. Light yellow is used for deserts, and white for ice and glaciers. So a map of Australia that is mostly yellow tells you at once that much of the continent is dry, while a strip of green along a coast shows low plains.

Scales, legends and coordinates

Maps also carry tools for reading them. A scale shows what real distance a length on the map stands for, for example 0 to 1,000 km. A legend explains the symbols used, such as a line for a route or a dot for a city, and the directions, north, south, east and west, show which way is which. A world map gives a good picture of shapes, sizes, locations and distances, but for precise work professionals use latitude and longitude, the grid of coordinates met in Grade 6, which can fix any place exactly. The rest of the chapter is in the Chapter 1 notes, the oceans in continents and oceans, and every question in the NCERT solutions.