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.