Maps and charts are printed as projections of the land onto a piece of paper. The Mercator projection shows what the world looks like when a light is placed in the center of a hollow earth, and it shines out through the surface of the earth to project the shape of land and sea onto a piece of paper wrapped around the globe. Thus, the north and south poles would have to be at an infinite distance from the equator on such a map, but the shape of the land at the equator would be correct. Greenland looks larger than it really is on a Mercator projection. The advantage of the Mercator projection is that it allows one to draw a straight ‘rhumb line’ between two points and have the bearing remain the same along that line. On a Maine chart, the longitude lines will be closer together than the latitude lines. The scale of nautical miles is the latitude scale on the right side of the chart, as one degree of latitude is equal to sixty nautical miles, or one minute of latitude is one nautical mile. While useful for the navigator, the projection greatly distorts the size of the land masses, and it is no longer used to show the whole world on a flat plane, however, it is used in large scale navigational applications. Source.