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).

Australia - Greenland overlay
The Mercator projection portrays Greenland as larger than Australia; in actuality, Australia is more than three and a half times larger than Greenland.

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. While sacrificing the size, it’s actually a really useful projection for navigation and on keeping the correct shape of countries.

Mercator projection
The Mercator projection shows courses of constant bearing as straight lines.

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

Another beautiful video on the same subject, titled “How the World Map Looks Wildly Different Than You Think”.

Why all world maps are wrong: making accurate world maps is mathematically impossible.

UPDATE: November 13 2017 – You can use the True Size Tool to see the true size of the continents/countries.

True size of Russia over Africa
Maps like this are based on cylindrical Mercator projection, which did good job with nautical purposes. The problem with this cylindrical projection is that when laid down flat the linear scale of a Mercator map increases with latitude, it distorts the size of geographical objects far from the equator and conveys a distorted perception of the overall geometry of the planet. You can visualize this with the True Size Tool. Here it is evident that Russia (dark blue) is just half the size of Africa, which Mercator Projection made implausible. You can also see the United States (light blue) and China (orange) over Africa.


Leave a Reply