# More on Projections

### Why projections are necessary?

Because of a **Developable Surface**, a geometric shape that forms a flat surface after unrolling is know as a developable surface.

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 features is preserved.

**Classification based on Preservation :**

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

**Preservation Projections**

of Area : Equal Area or Homolographic Projection

of Shape : Orthomorphic Projection

of Bearing : Azimuthal Projection

of Distance : Equidistant Projection

None : Aphylactic 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 Surfaces

Three View Points

Three Aspects

### 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.