A spherical co-ordinate system (like latitude and longitude) works well only if one is using a globe but not if one has to display the data on a flat surface like a map. Thus arises the need for projections.

Projection is a Conversion Tool that allows one to predict the type of distortion one would get going from three-dimensional spherical surface to the two-dimensional map surface, i.e. projection is a Geometric Transformation that converts latitude longitude co-ordinates into planar co-ordinates.

Projections can be based on developable surfaces such as a plane, cylinder or cone or on a mathematical function. Map projection was originally seen as positioning a light source inside a transparent globe on which opaque earth features were placed and then projecting the feature outlines onto a two-dimensional surface surrounding the globe. The surrounding surface may be Planar, Cylindrical or Conical.

Planar , Cylindrical & Conical Projections

● PROJECTION PROPERTIES:

1. Equal Area or Equivalent projection:
In projection, the area of a feature on the globe is depicted on a map having same area, although its shape may not be same. For e.g. a square on the earth’s surface might be a rectangle on a map but their areas are same.
Shape:
Projection ensures accurate portrayal of shape by preserving correct angular relationships such as parallels and meridians
always intersect at right angles. For e.g. Mercator projections.
Distance:
Projections maintain true distances in one direction or along certain selected lines. For e.g. equidistant projections show true distance from one or two central points.
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Related readings:

Map projections

Classes of Map Projection

Geographic Coordinate System

Datum, Ellipsoid, Rhumb Line, Secant, Spheroid, Tangent and other useful terms in Map Projection

Reference Datum of Earth