One of, if not the most well known map projection is the Mercator projection. It is a conformal cylindrical projection produced by Gerardus Mercator in 1569, and quickly became the primary map used for nautical navigation since a straight line on the map represents a constant course, which is arguably its most significant potential use. However, land masses that are farther away from the equator are more distorted in terms of area than land masses closer to the equator. As the map continued to gain popularity, it became the primary projection of the world typically found in US classrooms in the 20th century. This was critical, as the average person is not cognizant of the many distortions associated with map projections, and could believe that the sizes of certain countries and regions compared to others are accurately depicted. This is entirely false, and the relative sizes of regions like the United States, Russia, Africa, Greenland and Australia convey subtle messages that can subconsciously be interpreted as one region having "importance," or some other critical aspect, over another region. As a result, contemporary atlases no longer use the Mercator projection, and instead use equal-area projections more often than conformal ones. Along with the Mercator, another conformal projection is the Stereographic projection. It is advantageous when mapping the Earth's poles, and also has applications in photography when capturing wide-angle views.
Another significant type of projection is the equal are projection. As the name implies, it preserves surface area and accurately depicts the relative sizes of regions. An example is the Mollweide equal area projection, also known as the elliptical projection, which distorts angles and the accurate shapes of regions in order to maintain accurate relative sizes. Created in 1805 by astronomer Carl Mollweide, this particular projection is advantageous for mapping the entire globe, as well as the sky. As a result, the Mollweide projection is found in a great number of 19th century star atlases, and is frequently used to display astronomical observations, such as cosmic microwave background radiation in full-sky format. An additional type of equal area map is the Bonne projection. Named after Rigobert Bonne, this pseudoconical projection displays every parallel as an arc of a circle. Like the Mollweide map, the Bonne projection maintains accurate area, and distorts shape. These distortions are more severe farther from the center of the map, but are minimal towards the center. The scale is accurate along the straight, central meridian line.
Along with the equal area projections, another widely used projection is the equidistant projection, in which the distances from a standard line or point are preserved. One example is the azimuthal equidistant projection, which may have been used by ancient Egyptian star maps dating back to the 11th century. The main advantage of this projection is that all points on the map are at correct distances, as well as correct angles from the center point, which is commonly the north pole. This has various social advantages, as the United Nations uses this particular projection in their emblem, since there seems to be no implied "primary" countries or regions. The distortion of shapes and areas is present in this projection, and they are more extreme farther from the center of the map. Another equidistant projection is the conic equidistant one, which is derived from a conic section of the earth's surface. Distortion is minimal along the central parallel, and is constant along any given parallel. This type of projection is useful for displaying only one hemisphere, and is neither equal area or conformal. These six map projections described offer only a brief look at the vast variety of modern and old projections.
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