Map Projections

What is the map projection?

A map projection is a way to represent the curved surface of the earth on the flat surface of a map.

1)      To represent the curved surface of the earth on the flat surface of the paper.

2)      To minimize the distortions of the earth.

Types of map projections

1)      Cylindrical projections:

·         Wrap a piece of paper around the earth to form a cylinder and bisector from top to the bottom and flattened into a plane.  

·         Since cylindrical projections are tangent to the earth equator, there are no distortions along the equator of cylindrical projections.

·         But it distorts near the Polar Regions.

·         Therefore cylindrical map projections are most suitable for mapping the earth equator.

2)      Conic projections:

·         Wrap a piece of paper around the globe to form a cone and cut from apex to bottom and lay flat.

·         As conic projections are tangent to higher in latitude as the cone angle increases.

·         Therefore conic projections are most suitable for mapping mid-latitude areas.

3)      Planar/Azimuthal projections:

·         Place a piece of paper on a single point on the earth.

·         It used plot shortest distance between two points but landmasses are distorted away from the central points.

·         Since planar projections are tangent to northern and Sothern Polar Regions, patterns of area and shape distortion are circular about the focus.

·         Therefore planer projections are ideal for mapping Polar Regions.

Distortions of earth, a shape can be minimized by using map projections which have the same shape as a particular area of the earth.

                           

What are the distortions?

1)      Area: The size of a feature on a map is the same relative to its size on the earth.

           A larger area like America has relatively higher errors than that of the smaller areas like Sri Lanka.

2)      Distance: The distance from one point to another on a map is the same relative to its distance on the earth.

3)      Shape: If a map preserves the shape, then feature outlines (like country boundaries) look like the same on the map as they do on the earth.

4)      Direction: The degrees of angle from north to a given point on a map is the same relative to its angle one the earth.

Examples for distortion of world map

1) Distortions of Mercator cylindrical projection

2)      Distortions of Planar/Azimuthal projections: