The world is a three dimensional sphere (or ellipsoid or geoid) and to represent the world in two dimensions, map projections are used. There are three types of projections: planar/azimuthal (projected onto a plane), cylindrical (projected onto a cylinder) and conical (projected onto a cone), and three preserved properties: conformal (angles/shapes preserved), equidistant (relative distances are preserved) and equivalent (same proportional areas as Earth). Different projections preserve various properties, which are then used for varying purposes. Distortion between the Earth and the projection is inevitable, and it increases proportional to the plane-Earth distance. When selecting a projection, since distortion is minimized along standard lines (Earth-plane intersection), the one with the standard line(s) closest to the area in question is desired.
Conformal map projections locally preserve angles, as the parallels and meridians are perpendicular. This projection is used when observations/measurements regarding directions and/or shapes are taken. The two conformal map projections are the Cube and Mercator Projections. Azimuthal projections (projection onto a tangent plane) are said to be conformal, and the cube projection is a collection of azimuthal projections. The Mercator projection is a cylindrical projection, also preserving local angles and shapes. The distances from Washington DC to Kabul for the Cube and Mercator projections are very close (10117.16 mi and 10112.12 mi, respectively).
Conformal map projections locally preserve angles, as the parallels and meridians are perpendicular. This projection is used when observations/measurements regarding directions and/or shapes are taken. The two conformal map projections are the Cube and Mercator Projections. Azimuthal projections (projection onto a tangent plane) are said to be conformal, and the cube projection is a collection of azimuthal projections. The Mercator projection is a cylindrical projection, also preserving local angles and shapes. The distances from Washington DC to Kabul for the Cube and Mercator projections are very close (10117.16 mi and 10112.12 mi, respectively).
Cube Projection
Mercator Projection
In equidistant map projections, the distance from the center of projection to any other place is uniform. This projection is used when the map is used to make important distance measurements. The two equidistant projections are the Equidistant Conic Projection and Sinusoidal Projection. The first is a conic projection, and the second is a pseudocylindrical projection where the parallel distances are equidistant. The distances from Washington DC to Kabul for the Equidistant Conic Projection and Sinusoidal Projection are 6972.48 mi and 8098.08 mi, respectively.
Equidistant Conic Projection
Sinusoidal Projection)
Equivalent, or equal area map projections retain the same proportional areas as on Earth. This projection is used in the comparison of the various areas of Earth. The two equal area projections are the Bonne Projection and the Mollweide Projection. The first is a pseudoconical projection (the Sinusoidal projection is a variation of the Bonne projection), and the second is a pseudocylindrical projection that sacrifices angles and shapes to preserve area. The distances from Washington DC to Kabul for the Bonne and Mollweide Projections are 6730.70 mi and 7925.56 mi, respectively.
Bonne Projection
Mollweide Projection
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