The Mercator map of the world has been the most popular during the last few centuries because correct angles and shapes are preserved throughout the map. Its straight, parallel meridians allow angle measurement with a protractor. Consequently, it is particularly useful for both air and marine navigation. Its principal disadvantage is that distances are greatly distorted – Greenland appears larger than South America when it’s actually one-ninth the size. The extreme latitudes of the map are also exaggerated.