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 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

## 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.