A way of representing the earth’s curved surface on a flat surface of map is known as map projections. A globe represents the most accurate position, place of different things present on earth but a globe is not practical for many of the functions for which we require a flat map. Map projections help us to represent most of the earth’s surface at a wide variety of scales, on a flat, easily transportable surface. A globe is the true representation of distance, direction, area, shape, and proximity. A flat map distorts these properties for which a cartographer must see to that which characteristics to preserve, which to distort and how much distortion can be done. Henceforth, a flat map cannot have all the globe features. There are a much of unusual map projections. The process of transferring information from the Earth to a map causes every projection to misrepresent at least one aspect of the real world- either, shape, area, distance, or direction. Each map projection has advantages and disadvantages; the appropriate projection for a map depends on the scale of the map, and on the purposes for which it will be used. The properties of a map projection may also influence some of the design features of the map. Some projections are good for small areas, some are good for mapping areas with a large east-west extent, and some are better for mapping areas with a large north-south extent.
Map projections comprises many problems and techniques, including: *
Measuring Earth's shape and features
Collecting and storing information about terrain, places and people *
Adapting three-dimensional features to flat models (the main concern) *
Devising and designing conventions for graphical representation of data * Printing and publishing information.
If we compare the above two pictures, we could easily see that how the positions and scales of different areas of the earth has been which makes the globe reading and flat map readings different. Commonly used Map Projection Terms
Azimuth—The angle, measured in degrees, between a base line radiating from a center point and another line radiating from the same point. Normally, the base line points North, and degrees are measured clockwise from the base line. Azimuthal— A map projection in which the direction from a given central point to any other point is shown correctly is called a zenithal projection or Azimuthal projection. Aspect—The placement of a projection system relative to the Earth's axis. A polar aspect is tangent at the pole, an equatorial aspect is tangent at the Equator, and an oblique aspect is tangent anywhere else. Cartesian coordinate system —A coordinate system in which a point's location is described by its distances from a set of perpendicular lines that intersect at an origin, either two lines in a plane or three in space. Conformal— A map projection in which the angles at each point are preserved is known as Conformal. This means that the shapes of small areas are maintained accurately. The size of most areas, however, is distorted. Conic—A map projection where the Earth's surface is projected onto a tangent or secant cone, which is then cut from apex to base and laid flat. Cylindrical—A map projection where the Earth's surface is projected onto a tangent or secant cylinder, which is then cut lengthwise and laid flat. Datum—A reference for position on the surface of the Earth. In surveying, a datum is a reference system for computing or correlating the results of surveys. There are two principal types of datum: vertical and horizontal. A vertical datum is a level surface to which heights are referred. In the United States, the generally adopted vertical datum for leveling operations is the National Geodetic Vertical Datum of 1929. The horizontal datum is used as a reference for position. The North American Datum of 1983 is based on the Geodetic Reference System 1980 (GRS80) spheroid; it is an Earth-centered datum...
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