Map Projections
Map projection refers to the process of translating the three-dimensional surface of the earth on a two-dimensional map. It is the process by which every point on a globe can be moved when it is flattened. Compromises are made in accuracy, and some information gets lost since one dimension is ignored. Several types of projections have evolved to represent at least one feature (actual distance between places) accurately, even though at the cost of distorting other features like area, shape and compass directions.
How to Choose a Projection ?
Choosing the right type of projection is a perennial challenge for a cartographer. However, it is an accepted norm to choose a projection that preserves a particular spatial property that a map must accurately depict. Each projection preserves or compromises or approximates basic metric properties in different ways. The purpose of the map determines which projection should form the base for the map. Since several purposes exist for maps, many projections have been created to suit each purpose. The distortion factor, which is inevitable in any projection, has to be borne in mind. It is a conscious call that the cartographers have to take based on the understanding of the objective – whether to create a great-looking map or depict distances, directions, and areas accurately.
Major types of projections:
Cylindrical Projections
Considered the most common of all map projections, maps we see in atlases are generally based on cylindrical projection. In such a projection, a cylinder is wrapped around a globe. The image of the globe is projected onto the cylinder, which is later unwrapped and spread out. The various longitudes are mapped as parallel vertical lines. The downside of this projection is the distortion of shape and scale that happens at the poles, although the inaccuracy is minimal in equatorial regions.
Maps following cylindrical projections can be equal-area, conformal, or equidistant. The ones that accurately reflect area are called equal-area maps. Similarly, equidistant maps are those that correctly show the distance between points. The maps that maintain the shape of objects are referred as conformal maps. Mercator projection is one of the earliest specimen of cylindrical projections, which proved highly useful for navigational purposes.
Mercator Projection
Geradus Mercator, in a bid to help the navigators, invented his famous projection in 1569. He deliberately made the lines of latitude and longitude intersect at right angles to keep the direction of travel consistent. However, distortion in the map used to be felt while moving north and south from the Equator. According to his projection, Antarctica appeared to be a huge continent and Greenland appeared as large as South America. In reality, Greenland is hardly one-eighth of that continent.
Robinson Projection
In the 20th century, there was a gradual shift towards the rounded Robinson Projection. Devised by Arthur H. Robinson in 1963, this projection deliberately distorted various aspects of the map. It was neither equal-area nor conformal. This distortion, according to the creator, was necessary to produce a better overall view of the world. While the distortion was maximum near the poles, its severity declined as one moved closer to the equator.
Conical Projections
In order to overcome the challenges posed by the cylindrical projections, conical projections are used. With the introduction of conical projections, a new era of map projection heralded and accurate representation of the countries closer to the poles was made possible. For such a projection, the globe is imagined to be inside a cone. The apex of the cone is often aligned with the polar axis of the sphere. The different points get projected inside the cone. Unlike the cylindrical projections, the lines of latitude are represented by circular arcs. Maps of temperate zones are generally created based on conical projections.
Lambert Conformal Conic Projection
Developed by Johann Lambert around 1772, such a conical projection conforms to the original shape of a region. Considered as one of the best projections for middle latitudes, it represents shape more accurately than area. To think of it conceptually, a cone is seated over the sphere of the Earth and the surface is conformally projected onto the cone. This conic map projection is primarily used for aeronautical charts.
Azimuthal Projection
Azimuthal projection or planar projection assumes that the features of the globe will be projected on a flat surface. To begin with, it is important to understand what does an azimuth mean? Considering that the earth is a sphere, choose any point on it (Point A). From this point, take two points in different directions, provided they are equidistant from Point A. As you join both these points to Point A, an angle is formed between these lines. This angle is known as azimuth of the surface.
In an Azimuthal map projection, this angle is preserved. It certainly means one thing – the azimuth measured on a map would be the same as that measured on the sphere. It also ensures that the directions are preserved on the final map. Hence, the maps created from these projections can be used for making globes to accurately represent the earth. However, in azimuthal projection, the shape of an area can be more than distorted.
Gnomonic Projection
This is a derivative of the Azimuthal Projection and also the only map projection that shows great circles (meridians and the equator) on the sphere as straight lines. That way, it becomes easier to find the shortest distance between two points. Said to be developed in the 6th century B.C, the gnomonic projection is used in seismic work as seismic waves travel along great circles. Navies also use this projection for radio direction finding, since radio signals travel along great circles.
Other Projections
Pseudo-cylindrical and Pseudo-conical projections:
These are considered as minor variants of cylindrical and conical projections. For example, the pseudo-cylindrical and pseudo-conical projections have curved meridians, unlike the original projections.Hybrid Projection:
As the name suggest, a projection of this kind is generally a blend of several projections mentioned above. Hybrid projection is used to produce a map that will be used for a specific purpose.| World Maps in Different Themes |
Last Updated Date: February 16, 2017
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