The **mercator projection** It is a system for graphically representing the Earth’s surface on a plane, in order to make maps. Among the nearly 400 map projections that exist, Mercator’s is a type of cylindrical projection.

Gerardus Mercator, in 1569, imagined the Earth inside a cylinder whose diameter was equal to the terrestrial equator. Then he was projecting lines from the center of the Earth to the cylinder. Thus he was representing all the points of the contour of the terrestrial surface, which when united represent the lines of the geographical forms.

The maps obtained by this projection are especially useful for navigation charts, since it allows routes to be drawn using a straight line.

Its main advantage is that it represents geographical shapes very well, keeping the real angles. However, it alters the proportions of land areas as we move away from the equator.

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## Characteristics of the Mercator projection

### map projections

The Earth is similar in shape to a revolving ellipse (geoid, with flattened poles and a bulging equator). On this curved surface the contours of the continents and islands are presented.

This implies a difficulty when trying to represent that curved surface in a plane and for this geographers use projections. However, all projections generate some deformation or distortion with respect to reality and no method accurately represents the actual Earth surface.

Therefore, there are different types of cartographic projections, each one with advantages and disadvantages that can be flat, conical, cylindrical or polyhedral, among others. In this case, the Mercator projection is a cylindrical projection.

### cylindrical projection

To solve the problem of projecting the Earth’s surface onto the plane, Mercator imagined the Earth inside a cylinder of the same diameter. Where the major or longitudinal axis of said cylinder coincided with the terrestrial axis of rotation (normal cylindrical projection).

Subsequently, he was projecting imaginary lines from the center of the planet passing through each point on the contour of the earth’s surface until intercepting the cylinder. Thus, he was projecting each point of the map on the cylinder and by extending it as a plane and joining the points, he obtained a fairly exact image of the terrestrial contour.

In this case it is a conformal normal cylindrical projection, where shapes and angles are maintained. Like distances, but not so the relative proportions of surfaces in the plane.

### map orientation

The map built using the Mercator projection is also characterized by being oriented north upwards and with Europe occupying the center. Although this seems obvious due to the extensive use made of this map, the reality is that equally valid maps can be made from different perspectives.

## Applications

### Navigation

This type of map projection was designed by Mercator to create navigational charts (maps intended for use by sailors). Since then it has been used for this purpose, considering its facility to trace constant heading routes through straight lines.

### school purposes

On the other hand, its use has been generalized by using it as a real representation of the Earth in other areas. This is how we find it in textbooks, on school wall maps, and in many other contexts.

However, it has been pointed out that maps constructed using the Mercator projection should not be used for school teaching. This is due to the fact that they present a deformed relation of surfaces between continents.

Thus, the continents with the largest land mass around the equator maintain a relative surface on the map similar to the real one. However, the continents located north of the equator appear larger than reality.

It has been proposed that the 1885 Gall-Peters projection, which is an equidistant normal cylindrical projection, be used for school purposes. It saves surface proportions, constraining the Mercator projection for navigational charts, where its features make it efficient.

### Geographic positioning systems on the WEB

Online geographic location systems via the INTERNET, such as google maps, They use the Mercator projection. Specifically the so-called Web Mercator Projection or google web Mercator, which Google adopted in 2005, and became widespread among online map providers.

This is mainly due to the fact that the mathematical calculations required for its execution are simpler than those of other types of projections. As well as the fact that in this projection the angles remain as they really are.

## Advantages

The map made with the Mercator projection is ideal for plotting straight-line routes for navigation and includes a geometric formula to correct distortions by transforming measurements into degrees of latitude. On the other hand, this map projection keeps the angles between points as they really are.

In addition, as it was already pointed out, the Mercator projection has the great advantage of the lower complexity of the mathematical operations necessary for its realization.

## Disadvantages

The fundamental disadvantage of the Mercator projection for maps has to do with the ratios of the sizes of the land masses. Close to the equator the proportions are maintained, but moving away from the equator the areas increase with respect to reality.

This is because the projection was made on a cylinder, where only the equator is tangent to it, without compensating for the generated deformation. Points at the equator are parallel to the cylinder, while points far from it are not.

In the latter, the lines that project them intersect the cylinder at diagonal points and more separated from each other. Therefore, the parallels and meridians of the reference system or coordinates are extended to the north and to the south.

This brings as a consequence that when observing a map made with the Mercator projection, we see, for example, Alaska larger than Brazil. However, the reality is that Brazil is 5 times bigger than Alaska.

Just as it also gives the impression that the Iberian Peninsula is almost the same size as Venezuela or Colombia, when they are larger. Likewise, Russia on the Mercator map appears 7 times larger than Australia, when it only has a surface area twice that of this continent.

### the geographic poles

Another shortcoming of the Mercator projection is that on the generated map, both the north pole and the south pole lie outside the area. This is particularly problematic for the south pole, where the continent of Antarctica is located.

## References

Fernández-Coppel, IA (s(f). The UTM (Universal Transverse Mercator) projection. Geographic Locations. Higher Technical School of Agricultural Engineering. University of Valladolid.

Gomez-Moreno, RA (2004). Guide to cartographic projections. Statistics National Institute. Geography and Informatics. Mexico.

Miraglia, M., Flores, AP, Rivarola and Benitez, M., D´Liberis, M., Galván, L., Natale, D. and Rodríguez, M. (2010). Manual of Cartography, Remote Sensing and Geographic Information Systems. Geographic Information Systems Laboratory. Conurbano Institute. National University of General Sarmiento.

Raisz, E. and Mantero, JM (2005). General cartography. trad. 7th Omega edition, Barcelona.

Robinson, AH, Sale, RD, Morrison, JL, Muehrcke, PC, Ravella-Vives, JM, Ferrer, RM (1987). Cartography elements. 1st Omega Edition.