We explain what a cartographic projection is, its importance in creating maps and its properties. In addition, we give you examples of different types of projections.
What is a cartographic projection?
A map projection is a tool to represent the curved surface of the Earth on a plane. Because the Earth is a three-dimensional object, any attempt to map its surface will inevitably present some form of distortion.
It is a procedure of creating maps by cartographers who must be guided by the coordinate system that makes up the terrestrial parallels and meridians to construct a spatial representation that is faithful to the proportions of the planet's curvature.
This, however, cannot be done without a certain margin of error, so projections are studied in order to reduce distortion as much as possible and preserve, in particular, the three fundamental aspects of a map: distances, surfaces and shapes.
Characteristics of cartographic projections
The main characteristics of cartographic projections are:
- These are tools to represent the spherical surface of the Earth on a plane.
- They always produce a certain distortion in the distances, shapes or sizes represented.
- There are different types of projections: cylindrical, conical and azimuthal.
- The Mercator projection is the most used worldwide.
Properties of a cartographic projection
All cartographic projections present characteristic features that are linked to the type of transformation or the geometric procedure used to carry them out. So, A projection can meet one or two of the following properties, but in no case can it meet all three at the same time:
- Equidistance. The projection is faithful to the distances of the original and maintains its proportion at the corresponding scale throughout most of the map. In some sectors, distortion of distances is inevitable and areas and shapes appear altered.
- Equivalence. The projection is faithful to the surface areas of the original, that is, it does not distort the extension, but the shapes may be modified.
- Accordance. The projection is faithful to the shapes and angles of the original, that is, it does not distort the silhouette or appearance of the surface represented, but the sizes are distorted.
The choice of one cartographic projection or another depends on the specific needs of the map and the geographical properties that you want to highlight or preserve.
Types of cartographic projections
To classify cartographic projections, the criterion of the geometric figure that inspires it is generally used:
- Cylindrical projections. These are projections that use an imaginary cylinder as the surface of the map. These projections more faithfully respect the shapes, but as the distance to the equator increases, a greater and more noticeable distortion of distances and surfaces occurs. The Mercator projection, the most used worldwide, is a type of cylindrical projection.
- Conic projections. In a similar way to cylindrical projections, these projections are obtained by placing the Earth's sphere within the interior curvature of an imaginary cone, on which the parallels and meridians are projected. These projections convert the meridians into straight lines starting from the pole and the parallels into concentric circles within the cone. The map obtained is ideal for representing the middle latitudes, because the distortion increases as you move towards the poles. An example of a conic projection is the Lambert projection.
- Azimuthal projections. Also called zenith projections, they are obtained by placing the Earth's sphere on an imaginary plane, tangent to the sphere itself (as if looking at the planet from above), on which the meridians and parallels are projected. These projections are more faithful in high latitude regions, but present increasing distortion the greater the distance to the poles, so they are not used to represent middle latitudes or the equatorial region.
Examples of cartographic projections
The main and best-known cartographic projections are:
- The Mercator Projection. Created by the German geographer and mathematician Gerardus Mercator (1512-1594) in 1569, it is one of the most used terrestrial projections in history, especially in the making of maps for navigation during the 18th century. It is a cylindrical type projection that respects the shape of the continents, but noticeably distorts the sizes, especially in those regions far from the equator. For this reason, for example, Greenland appears the same size as Africa, when in reality Africa is fifteen times larger.
- Lambert's projection. Also called the “Lambert conformal projection”, it was created in 1772 by the Franco-German physicist, philosopher and mathematician Johann Heinrich Lambert (1728-1777). This is a shape-maintaining conical projection, which is useful for topographic and weather maps, and is particularly suitable for mid-latitude regions.
- The Gall-Peters projection. Created by the Scottish clergyman James Gall (1808-1895) in 1855, this projection first appeared in the magazine Scottish Geographical Magazine. Its popularization and implementation corresponded to the German filmmaker Arno Peters (1916-2002) more than a hundred years later, in 1973, and for that reason it bears the name of both. This projection avoids exaggeration of the areas of high latitude regions, as occurs in the Mercator projection, but distorts the shapes, stretches the areas near the equator and compresses the areas near the poles.
- Van der Grinten's projection. Created in 1904 by the German-American cartographer Alphons J. van der Grinten (1852-1921), it presents the entire globe in a circle. It is neither conformal nor equivalent, but rather attempts to minimize distortions in shape, area and distance in a large part of the map, although it presents strong alterations in the polar areas.
- Aitoff's projection. Proposed in 1889 by the Russian cartographer David Aitoff (1854-1933), it is a zenith or azimuthal projection that is not very equivalent and does not conform, built from the distortion of the horizontal scale to turn the terrestrial sphere into an ellipse twice as wide as high.
- Robinson's projection. Created in 1963 by the American geographer Arthur H. Robinson (1915-2004), it emerged in response to the debate that occurred in the mid-20th century about a fairer representation of the planet. Its purpose was to show the world map in a simple way, so that it is neither equidistant nor equivalent nor conformal, but rather assumes its distortions (the most important in the polar region and in high latitudes).
- The Winkel-Tripel projection. This is a modified azimuthal geographic projection, proposed by Oscar Winkel in 1921, based on the combination of the Aitoff projection and an equidistant cylindrical projection. It was adopted by the National Geographic Society in 1998, and since then it has been considered the best model for terrestrial representation.
To take into account: Although the Mercator projection is the most used for creating world maps, it receives a lot of criticism for being considered Eurocentric. This is because Europe is located at the top and in the middle of the image, the northern hemisphere appears dominantly located in the upper plane and the southern hemisphere is arranged in the lower plane, in the lower part of the image.
Why do cartographic projections present distortions?
The Earth is a spheroid, that is, it has a curved shape in three dimensions. When you try to capture this curved surface on a two-dimensional plane, such as a sheet of paper or a screen, you must “unroll” or “flatten” that surface.
When converting a curved surface to a plane, geometric transformations are used that inevitably alter some geographic properties. The phenomenon of distortion is inevitable in any type of projection. This is because it is impossible to faithfully convert a spherical surface into a flat one and preserve its distance, shape, and surface aspects.
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References
- Esri. (sf). About map projections. https://desktop.arcgis.com/
- Garmendia, C. (2020). Cartographic projections: what should I know? Idecor. https://www.idecor.gob.ar/
- National Geographic Institute. (sf). Cartographic projections. Didactic Atlas. https://educativo.ign.es/
- Mettatec. (2023). Cartographic projections and their types. https://mettatec.com/
