Map projection is a process of mathematical conversion whereby a 3 dimensional world is transformed into a 2 dimensional world. Map projection is extremely useful as it allows us to stored data of our 3 dimensional world in a flat plane map. However, this transformation inherently causes distortions. The extend of this distortions depends on the way the map is projected. As shown in the above diagrams, the distances for Washington, D.C. to Kabul varies depending on the map projection.
No perfect map projections exist. Rather, there are thousands of different projections and each serves certain specific purpose only. Many of these map projections preserves certain properties of a 3 dimensional map. Some of these properties are shape, direction, area and distance. We need to be extremely careful in choosing the right type of projection for the job. For example, the World Azimuthal Equidistant projection, which preserves distance and direction from the center point, is used by radio operators to find out where to point their antennas to and what wavelength to use depending on the distance. The Mercator projection is used by navigators to plot their course as it preserves direction.
Note that the 2 equidistant projections presents vastly different distances. This is because the World Two Point Equidistant projection have two control points in which distances from any point on the map to the two control points are preserved. However in a World Azimuthal Equidistant projection, only distances and direction from the center of the map is preserved. Since neither Kabul nor Washington is at the center of the World Azimuthal Equidistant projection, the distances between the two cities is not preserved and hence inaccurate.
The preservation of specific map properties are not always important in map projections. Some commonly used projections do not preserve any properties of 3 dimensional maps. One example would be the Robinson Map projection. It is commonly used in textbooks in Singapore. The projection intentionally abandoned preserving any property for a compromise that results in a better world view. Maps may even be even be deliberately distorted for illustration or propaganda purposes. The preservation of metric properties may also not be as important in small area maps (ie. street maps etc.) as distortions are negligible.
No perfect map projections exist. Rather, there are thousands of different projections and each serves certain specific purpose only. Many of these map projections preserves certain properties of a 3 dimensional map. Some of these properties are shape, direction, area and distance. We need to be extremely careful in choosing the right type of projection for the job. For example, the World Azimuthal Equidistant projection, which preserves distance and direction from the center point, is used by radio operators to find out where to point their antennas to and what wavelength to use depending on the distance. The Mercator projection is used by navigators to plot their course as it preserves direction.
Note that the 2 equidistant projections presents vastly different distances. This is because the World Two Point Equidistant projection have two control points in which distances from any point on the map to the two control points are preserved. However in a World Azimuthal Equidistant projection, only distances and direction from the center of the map is preserved. Since neither Kabul nor Washington is at the center of the World Azimuthal Equidistant projection, the distances between the two cities is not preserved and hence inaccurate.
The preservation of specific map properties are not always important in map projections. Some commonly used projections do not preserve any properties of 3 dimensional maps. One example would be the Robinson Map projection. It is commonly used in textbooks in Singapore. The projection intentionally abandoned preserving any property for a compromise that results in a better world view. Maps may even be even be deliberately distorted for illustration or propaganda purposes. The preservation of metric properties may also not be as important in small area maps (ie. street maps etc.) as distortions are negligible.
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