Map Projections

Why are they important?

Since map making is about the representation of what we see, we need a surface that is producible on a flat surface. To make it more clear geometrically it is impossible to represent a sphere on a flat surface without distortions.

When that shape is a ‘Geoid’ (that’s what we call our Earth) with three-dimensional features the process becomes even more complicated and the only option we have is to make a compromise.

Therefore it becomes important to choose our compromises rightly. We should know the purpose of the map construction to preserve the right attributes and let go of others.

A developable surface is a geometric shape that forms into a flat surface after unrolling.

A sphere is not developable surface but is the closest geometrical form to the shape of the earth i.e., the Geoid. The shapes that form a developable surface are 2-dimensional geometric shapes like the Cone, Cylinder, Circle.

When we construct maps there are four geographical characteristics that we try to represent: Area, Shape, Bearing and Distance. There can also be a fifth type where none of the above feature is preserved. 

Classification based on preservation :

Based on these attributes following types of projections can be made…

Preservation Projections
of areaEqual Area or Homolographic Projection
of shapeOrthomorphic Projection
of bearingAzimuthal Projection
of distanceEquidistant Projection
noneAphylactic Projection

Perspective Map Projections

Classification on the basis of Development :

Are presented on a developable surface geometrically from a point, these are of three types

(i) Cylinder. (ii) Cone (iii) Plane

Three Viewpoints or the position of the light source

( i ) Centre (Gnomonic Projection) ( ii ) Periphery or antipodal (Stereographic Projection) ( iii ) Infinity (Orthographic Projection)

Aspects of Projection

(i) Polar  (ii) Equatorial or Transverse (iii) Oblique

Three Aspects
Three Surfaces 
Three View Points

Non-Perspective Map Projections

Are projections which are highly modified to a great extent for a specific purpose due to which they don’t remain geometrical anymore. Such projections are highly useful as they are modified for a specific purpose.