What is map projection?
Map projection is defined as the systematic drawing of a network or graticules of parallels and meridians on a developable surface portraying a part or whole of the earth’s surface with a specific scale and in accordance with a set of geometric and mathematical principles to satisfy certain objectives of the user.
Hence, a map projection is a technique by which we can represent the three-dimensional figure of the earth on a two-dimensional paper or plane.
Elements of map projection:
- Reduced earth:
A three-dimensional model of the earth with a reduced scale which can be developed on a flat sheet of paper is called reduced earth. The reduced earth should be more or less spheroid having the length of polar diameter lesser than equatorial and on this model, the graticules or network of lines of latitude and lines of longitude can be transferred on a developable surface.
- Parallels of latitude:
The circles running east-west direction around the globe, parallel to the equator are called Parallels of latitude or lines of latitude or Parallels. The inter-parallel distance is equal. Earth parallel lies wholly in its plane, which is called the plane of the parallel which is at a right angle to the axis of the earth and parallel to the equatorial plane. Parallels are not of equal length. They range from a point at each pole to the great circle at the circumference of the globe at the equator. Parallels are demarcated from 0⁰ to 90⁰ North and south latitudes.
- Meridians of Longitude:
The half-circle or semi-circles drawn in a north-south direction extending from one pole to the other is called meridians of longitude or meridians. The two opposite meridians make a complete circle, which encircled the circumference of the globe. Each meridian lies wholly in its plane, but all intersect at a right angle along the axis of the globe and perpendicular to the equatorial plane. There is no obvious central meridian with unique characteristics like the equator, but for convenience to draw all other longitudes an arbitrary choice is made, namely the meridian of Greenwich, which is demarcated as 0⁰ longitudes.
Properties of map Projection:
When three-dimensional earth is represented on a flat surface some distortion always occurred. In a map projection, it is always desired to preserve all the properties. But it is impossible to keep all the properties in a single projection. In preparing a map projection the following basic properties of the three-dimensional earth are to be preserved by using different methods.
- Equidistance: Distance between any two points of the map corresponds to the concerning points on the earth’s surface.
- Orthomorphic or True-Shape: Shape of the region represented on the map.
- Equal Area or Homolographic Projection: Size or area of the region corresponds to the mapped area.
- Azimuthal or true bearing: The direction in between any two points of the region corresponds on the map.
Classification of Map Projections:
Map projection varies with the size and location of different areas on the earth.
S0ME SELECTED MAP PROJECTION WE WILL DISCUSS:
- Simple Conical Projection with one standard parallel;
- Cylindrical Equal Area Projection;
- Mercator’s Projection;
- Bonne’s Projection;
- Polar Zenithal Stereographic Projection.
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