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...
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
(ii) Equatorial or Transverse
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.