# Maps can be deceptive

The standard maps we see every day use Mercator Projection, a cylindrical map projection presented by the Flemish geographer and cartographer Gerardus Mercator in 1569. It developed for navigational purposes, has often been used in world maps. And like all other type of projections, it can be deceptive.

In fact, every map tells lie, since it’s impossible to transform perfectly the three-dimensional world into two-dimensional surfaces like paper or computer screen. Map projections are necessary for creating maps and every map projections distort the surface in some fashion (a map projection is a systematic transformation of the latitudes and longitudes of locations on the surface of a sphere or an ellipsoid into locations on a plane).

One measure of a map’s accuracy is a comparison of the length of corresponding line elements on the map and globe. Therefore, by construction, the Mercator projection is perfectly accurate, k=1, along the equator and nowhere else. At a latitude of ±25° the value of sec φ is about 1.1 and therefore the projection may be deemed accurate to within 10% in a strip of width 50° centred on the equator. Narrower strips are better: sec 8°=1.01, so a strip of width 16° (centred on the equator) is accurate to within 1% or 1 part in 100. Similarly sec 2.56°=1.001, so a strip of width 5.12° (centred on the equator) is accurate to within 0.1% or 1 part in 1,000. Therefore the Mercator projection is adequate for mapping countries close to the equator.

But the Mercator projection is not completely unsuccessful. The projection preserves “true compass bearings between any two points” and that’s why it has become a standard in nautical navigation.

For some fun facts about the world maps using the Mercator Projection, you can watch the video below.