What is Map Projection?
In cartography, the flat, 2D representation of globe in order to make a map is map projection. When a spherical object is flattened, its alignment will definitely get distorted. But, map projections help us in obtaining the earth’s map systematically. There are multiple ways to project the surface of Earth. To understand the concept, consider an orange and imagine its peeled skin to be flattened on surface; you may have to stretch it or tear it.
(Source: Anji Reddy, Remote Sensing and Geographical Information system)
While getting a projection some of the properties will be preserved but some may get distorted.
Likewise, considering conformal projection; shape will be preserved but area won’t, this property is known as Conformality.
With equal area projection area will be same but the shape gets distorted and this property is known as Equivalency.
Other property is distance; in most of the projections, distance gets distorted, e.g. eqirectangular projection, but where distance is preserved the property is called as Equidistant.
Azimuthal Equidistant Projection
In order to preserve any one of these properties, the other two will definitely get distorted.
Classification of map projection
To understand the types in a better way let’s consider a light source kept inside the Earth in order to get the shadows of latitudes, longitude and continents on a paper. The light can be placed in different position like at the centre, on the top etc.
Few of the projections which are commonly used are classified under three families; Cylindrical, Conical and Azimuthal.
Consider a paper wrapped cylindrical on the globe and then it is straightened.
Pseudo-cylindrical projections (Robinson )
Robinson is a pseudo cylindrical projection, which was created in 1963. Pseudo cylindrical projections are considered best where the earth is displayed with a curved edge and curved meridians. Generally, pseudo-cylindrical projections are equal area and are suitable for thematic or distribution mapping. Examples: Mollweide, Sinusoidal, Eckerts I–VI, Winkel I–II, Robinson
These are cylindrical conformal projections. Transverse Mercator was created in 1772. These are best used for the areas with a north south orientation.
It is a conformal projection created in 1569, which is widely used for navigation. The straight lines represented on maps are compass bearings.(rhumb line). At high latitudes (>70°), gross distortion is observed.
Mercator Projection (Cylindrical)
Cylindrical projections are also classified as normal, transverse and oblique projections, using lines of latitudes as line of contact, using meridians and using any other great circle line respectively.
Gnomonic Projection is the only projection where the shortest distance (great circle) between any two points is always represented by a straight line. This projection suffers from large scale distortions and is neither conformal nor equal area. Gnomonic is created in 6th century BC and said to be the oldest projections. These are used to plot radio signals and radio waves.
Gnomonic Azimuthal Projection with geogebra
It is conformal projection which is considered as the oldest of all the projections. The very first record of this is from 150 AD. It is widely used for mapping areas that are roughly circular in shape. Scale distortion is moderate.
The interesting fact about stereo-graphic projection is that any line passing through the centre is a great circle.
It is a perspective projection with its viewpoint at infinity and is a parallel projection lines.
Some other azimuthal projections are
Azimuthal Equidistant; Mostly used for air-route distance maps.
Lambert Azimuthal Equal Area; frequently used for thematic mapping of continents or regions.
In order to understand this, wrap a piece of paper around the globe to form a cone. Now, lit a torch from the centre of the Earth. The shadow on the surface will give the conical representation of the globe.
Lambert Conformal Conic
The only conformal conic projection which is used for topographic mapping at a regional or continental level. It was created in 1772. Other applications are in making aeronautical charts, portions of the State Plane Coordinate System, and many national and regional mapping systems.
Albers Equal Area
Considered as the most important equal area conic projection; it is best suited for the region comes in the mid-latitudes. Two standard parallels are used in Albers equal Area projection.
There are some other projections like Interrupted Projections and Myriahedral Projections which are widely used.
Anji Reddy, Remote Sensing and Geographical Information system