The Mercator projection is most often used to produce flat maps of the World, where the globe we live on in fact is not flat at all. The drawback with the Mercator projection is that it distorts the shape and areas of large land masses, and the distortion gets progressively worse closer to the poles.
Africa looks about the same size as Greenland under the Mercator projection, which is very far from reality. Africa is really much bigger than it looks on most maps. Some years ago, The Economist published a map of “the true size of Africa”, where other countries and continents are located within the continental borders of Africa. See the map below and click on the image to see a larger version.