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.
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.
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.