The cylindrical projection in cartography it is one in which the points on the spherical surface are projected onto a cylinder, whose axis coincides with the line that passes through the poles and is tangent or secant to the sphere. The cylinder is a surface that can be opened in a plane forming a rectangle, without the lines projected on it suffering deformation.
There are several cylindrical projections, in which the parallels become horizontal lines and the meridians vertical lines, once the cylinder has been extended in a plane. In general, the projection cylinder is chosen such that it is tangent to the Earth's equatorial line. In this case its radius will be equal to the equatorial radius, see figure 1.
However, projection cylinders can also be chosen secant to two parallels equidistant from the equatorial line, in this case the cylinder will have a radius less than the equatorial radius.
The resulting map of the cylindrical projection will then present a grid of horizontal parallels and vertical meridians forming right angles..
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There are several types of cylindrical projections used in cartography, each with its strengths and weaknesses. In any case, the choice of a type of projection will depend on the final purpose of the map..
To begin with, an advantage of this and any other cartographic projection is that through them you can visualize portions of the Earth on a flat surface and take them with you to consult them easily..
The cylindrical projection is very suitable for world maps, since both hemispheres can be represented, unlike other projections, such as the conical projection, which only allows the representation of one of the hemispheres.
Now, when representing a spherical surface on a plane, it will always be distorted in one way or another. In the case of the cylindrical projection, the least distortion occurs in the intertropical zone.
Precisely with the purpose of taking advantage of the virtues of this type of projection, but at the same time trying to minimize these inconveniences, geographers have proposed different types of cylindrical projection over the centuries..
The invention of this projection is attributed to the Belgian cartographer, geographer and mathematician Gerardus Mercator in the year 1569. It is one of the most widely used projections on world maps, even today..
Its main virtue is that a constant direction route is represented on the map by a straight line.
Because of this unique feature, it was the type of map that navigators adopted shortly after it was released. It is then a conformal projection, because it preserves directions and angles.
But it is precisely this that makes the Mercator projection not conserve the areas. Regions outside the tropics, and especially those far north or far south, look exaggeratedly large..
Since its inception, the Mercator projection has been widely used to represent world maps with continents and countries..
Recently, a conspiracy theory has spread through social networks, which affirms that rich countries are interested in this type of projection, in order to appear larger and stronger on the world map than poor countries in tropical regions. This type of argumentation is a total fallacy.
The problem with the cylindrical projection, as we have seen in the previous sections, is that the scale is distorted away from the equator or the reference parallels, also known as standard parallels..
The main disadvantage is that outside the intertropical regions, this distortion of shapes and distances is increasing, increasing said deformation for the polar latitudes, making these territories appear much larger than they really are..
For this reason, modifications have been implemented to eliminate distortion as much as possible, emerging variants in the cylindrical projections, whose main characteristics appear below.
It is a variant of the classic Mercator projection that has become the standard mapping system for the web. This is the system adopted by Google in 2005 for its popular applications, Google Maps and Google Earth..
Other major internet map providers such as Bing Maps, Mapquest, OpenStreetMap, Mapbox and others have adopted this projection system..
The difference between the original Mercator projection and this type of projection is very subtle and the final result varies very little..
In the original projection the Earth is assumed to be a sphere, whereas in the Web - Mercator the Earth is assumed to be ellipsoidal..
However, there are countries that have not adopted these improvements in their maps. For example, for the continental United States and Canada, the Lambert Conformal Conic projection is preferred for air navigation charts and the Albert Conic projection for cadastre matters..
It is a cylindrical projection proposed in 1772 by the Swiss mathematician and geographer Johann Heinrich Lambert (1728-1777). In his original version, Lambert uses the equatorial line as a reference parallel.
In this type of projection, the aim is to correct the distortion in the area introduced by the Mercator projection, which is why it is also known as a cylindrical projection of equal area..
The constancy in the area in the Lambert projection is achieved at the cost of a deformation in the aspect, mainly in the regions of large values of latitude.
From this type of projection, a family of at least seven variants has emerged, in which two parallels equidistant to the equatorial line are chosen, keeping the invariance in the area as a fundamental characteristic but minimizing the deformation in the latitudes of interest of according to the use of the map.
In addition to those already reviewed, there are other types of cylindrical projections, even quite old. Some of them are described below.
It is a type of simple projection in which the meridians of the earth's sphere become equally spaced vertical lines. In a similar way, the parallels or circles of latitude become horizontal lines that are also equidistant..
This type of projection is very ancient and is attributed to Marinus of Tyrios, a Greek geographer who lived between AD 70 and AD 130. C.
This type of projection has the disadvantage that it deforms the areas and the forms mainly in the zones of latitude higher than that of the tropics, flattening the forms horizontally near the polar regions..
This type of projection therefore does not preserve the areas and angles, except in the equatorial parallel where it is exact.
It was proposed by the cartographer Osborn Maitland Miller (1897-1979) in 1942 using the equator as the standard parallel of the projection cylinder..
This projection is very similar to the Mercator projection, but with the disadvantage that it is not compliant, that is, a fixed heading on a Miller map looks like a curve..
To carry out his projection, Miller started from the Mercator projection, multiplying the real latitude by the factor ⅘ and then carrying out the Mercator projection. To compensate the factor at the projected latitude, it is multiplied by the inverse factor, that is, 5/4.
The result is that the forms at high latitudes suffer less distortion compared to the original form..
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