The types of map projections and their essence

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2018-04-02 03:58:17

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Geographical maps people use since ancient times. The first attempts to portray the surface of the Earth were made in Ancient Greece such scholars as Eratosthenes and Hipparchus. Of course, since cartography as a science is well advanced. Modern maps are created using satellite survey and using computer technology, which, of course, increases their accuracy. And yet, on every geographical map has some distortion relative to natural shapes, angles or distances on the earth's surface. The nature of these distortions and, consequently, the accuracy of the map depends on the types of map projections used to create a particular card.

The Concept of map projection

Let us Examine in more detail what map projection is and what their species are used in modern cartography.

why map projections represent in a distorted form

Cartographic projection – image of the surface of the Earth on the plane. Deeper from a scientific point of view, the definition: map projection – how to display points on the surface of the Earth on a plane, in which between the coordinates of corresponding points are displayed and the displayed surfaces installed some analytical dependence.

What is a map projection?

Construction of all types of map projections occurs in two stages.

  1. First, a geometrically irregular surface of the Earth appears on some mathematically correct surface, called the surface of relevance. For the most accurate approximation of that as most commonly used geoid – geometric solid bounded by the surface water of the seas and oceans, linked (sea level) and having a common water mass. At every point the geoid surface gravity is applied normally. However, the geoid and physical surface of the planet, also cannot be expressed by a single mathematical law. Therefore, as a surface relevance instead of taking geoid ellipsoid of rotation, giving it the maximum similarity to the geoid using the degree of compression and orientation in the body of the Earth. Call it the body of the earth or ellipsoid reference ellipsoid, and in different countries they take different parameters.
  2. Secondly, the accepted surface relevance (datum) is projected onto a plane using one or another analytical subject. Finally we get a flat map projection of the earth's surface.

Distortion projections

And you wonder why they are on the map the outlines of the continents are slightly different? On some map projections, some part of the world look bigger or smaller relative to any reference points than others. It's all in the distortion, which is the projection of the Earth transferred to a flat surface.

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principal map projections

But why a map projection displays in a distorted way? The answer is quite simple. The spherical surface is not possible to deploy on the plane to avoid creases or tears. Therefore, the image cannot be display, to avoid distortion.

Methods of obtaining projection

Studying map projections, their types and properties is necessary to mention methods of their construction. So, a map projection obtained using two basic methods:

  • Geometric;
  • Analytic.

Based on Geometric method are the laws of linear perspective. Our planet is conditionally accepted by the sphere of a certain radius and is projected on a cylindrical or conical surface, which can either touch or dissect it.

types of map projections

Projection obtained in this way are called promising. Depending on the position of the observation point relative to the Earth surface perspective projection is divided into types:

  • Gnomonics or Central (when the view is aligned with the center of the earth's sphere);
  • Stereographic (in this case, the observation point located on surface relevance);
  • Orthographic (when the surface is observed from any point outside of the sphere of the Earth; the projection of the constructed transfer points of a sphere with parallel lines that are perpendicular to the display surface).

Analytical method construction of cartographic projections are based on mathematical expressions linking the points on the sphere of relevance and the plane of the display. This method is more versatile and flexible, allowing you to create arbitrary projections of a predetermined character of the distortion.

Types of map projections geography

To create the maps used many kinds of projections of Land. Their klassificeret on various grounds. In Russia used classification Kavrayskaya, which uses four criteria that define the basic types of map projections. As the characteristic classification parameters are used:

  • The nature of the distortion;
  • Display form the coordinate lines of the normal grid;
  • The location of the point of the pole in the normal coordinate system;
  • Method implementation.

So, what are thekinds of map projections according to this classification?

Classification of projections

The following is a classification of map projections, with examples, on the basis of these basic criteria.

Distortion

As mentioned above, the distortion, in fact, an inherent property of any projection of the Earth. Distorted can be any surface characterization: length, area or angle. The type of distortion are:

  • Conformal or conformal projection, in which the azimuths and angles are transferred without distortion. Grid in conformal projection is orthogonal. The card thus obtained, it is recommended to use for definition of distances in any direction.
  • Equal-area or equivalent projection, which remains the area scale, which is taken to be equal to one, i.e., area is displayed without distortion. These cards are used for the comparison areas.
  • Equidistant or equidistant projection, the construction of which the zoom remains one of the main areas which be accepted rare.
  • Arbitrary projection, which can contain all types of distortion.

Form to display the coordinate lines of the normal grid

This classification is the most intuitive and therefore the most easy to understand. Note, however, that this criterion only applies to projections normally oriented to an observation point. So, based on this characteristics, the following types of map projections:

Circular, where the meridians and Parallels are circles, and the equator and Central Meridian of the grid in straight lines. A similar projection is used to image the surface of the Earth as a whole. Examples of circular projections can serve as a conformal projection of the Lagrangian, and the arbitrary projection of Grinten.

Azimuth. In this case, the Parallels are concentric circles, and meridians in the form of a beam moving radially from the center of the parallel lines. Such kind of projections is used in an upright position for displaying the poles of the Earth with the surrounding area and in the transverse as everyone familiar with the geography maps of Western and Eastern hemispheres.

types of map projections in the geography

Cylindrical, where meridians and Parallels are straight lines intersecting normally. With minimal distortion displays of the area adjacent to the equator or stretched along a certain standard of latitude.

what are the different types of map projections

Conical, representing a scan of the lateral surface of the cone, where the lines Parallels are arcs of circles with center at the apex of the cone, and the meridians – guides diverging from the vertex of the cone. These projections most accurately depict the territory lying in the middle latitudes.

the map projection types and properties

Pseudokoningii projection is similar to conical, but only meridians in this case, are represented curves which are symmetrical about the straight Central Meridian of the grid.

Pseudocylindrical projection resemble cylindrical, just as in pseudokoningii, meridians are represented curves which are symmetrical to the axial rectilinear Meridian. Used to image the Earth as a whole (for example, an elliptical projection Mollweide, is equal to the sinusoidal Sanson, etc.).

what is a map projection which their types

Polyconic, where the Parallels are drawn as circles whose centres are located on the middle Meridian of the grid or its sequel, the Meridian curves, are symmetrical rectilinear axial Meridian.

The position of the point of the pole in the normal coordinate system

  • Polar Or normal – the pole of the coordinate system coincides with the geographical pole.
  • Cross Or transversion – the pole of the normal system coincides with the equator.
  • Slant Or tilting – the pole of the normal coordinate can be in any point between the equator and the geographical pole.

Usage

According to the method of use there are the following types of map projections:

  • Solid – the projection of all areas on the plane produced by a single law.
  • Multilane – mapped area is conditionally divided into several latitudinal zones, which are projected on the plane of the display by a single law, but change the settings for each zone. An example of such a projection can serve as a trapezoidal projection Muffling, which was used in the USSR for large-scale maps until 1928
  • Polyhedral – the territory is conditionally divided into a number of zones according to longitude, projected onto the image plane produced by a single law, but with different parameters for each zone (for example, projection Gauss-krüger).
  • Part when some part of the territory is mapped to the plane using one pattern and the remaining area on the other.

The Advantage of a multi-band and multi-facetedprojection is a high-fidelity within each zone. However, a significant drawback is the inability to obtain a continuous image.

Of Course, each map projection can be classified using each of the above criteria. So, the famous projection of the Earth on the Mercator is a conformal (conformal) and transverse (transversional); projection Gauss-krüger – conformal transverse cylindrical, etc.


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Alin Trodden - author of the article, editor
"Hi, I'm Alin Trodden. I write texts, read books, and look for impressions. And I'm not bad at telling you about it. I am always happy to participate in interesting projects."

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