Map Projection and Coordinate System

Dr. Rohit GoyalProf., Civil EngineeringMalaviya National Institute of TechnologyJaipur

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Topics CoveredGeographic Coordinate SystemWhat is Map ProjectionProperties of Map ProjectionCategories of Map Projection

Perspective Non-Perspective

Surface of Projection SystemsAspect of Projection Systems

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Geographic Coordinate System To locate a point on earth, we use network of

latitude and longitude (known as graticule). Equator is used as a reference point for

measurement of vertical angle , called latitude (, in next figure). Equators latitude is 0o and that of north pole is 90oN, south pole is 900S.

Meridian passing through Observatory of Greenwich in Great Britain has been adopted as the Prime Meridian, which is used as the origin to measure the horizontal angle, known as longitude (). Locations towards east from Greenwich are considered as +ive and expressed as oE and that on west are considered –ive and expressed as oW.

India lies approximately between 68oE to 96oE longitude and 7oN to 37oN latitude.

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Graticule

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Map Projection For the representation of the entire surface of

the earth without any kind of distortion, a map must have a spherical surface. A map of this kind is known as a globe.

A flat map (2-Dimensional) cannot accurately represent the rounded surface (3-Dimensional) of the earth except for very small areas where the curvature is negligible. However such transformations can be achieved in

variety of ways by compromising on selected properties and preserving required properties.

A “Map Projection” is a systematic representation of all or part of the surface of a round body, especially earth, on a plane (Snyder, 1987)

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Properties of Projection System Four properties of importance for any projection

system are Area Shape Distance Direction

None of the 2-Dimensional projection system can preserve all the properties

All the different map projection systems are designed to produce the network of meridians and parallels that can achieve one or two of these properties.

Maps preserving area are known as “equal area” or “equivalent”, that preserving shape are known as “conformal” or “orthomorphic”, that preserving distance are known as “equidistant”.

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Categories of Map ProjectionsMap projections can be

classified as Perspective or geometric

•Geometric projections are classified according to the type of surface on which the map is assumed to be developed, such as cylinders, cones, or planes

Non-perspective or analytical•Analytical projections are developed

by mathematical computation.

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Perspective Projection SystemsThese are characterized by the use

of a viewpoint (point of origin) and surface of projection Viewpoints could be in the centre of

globe, at an infinite distance (so that rays are parallel) or on the opposite side of the surface, as shown in next figure.

Accordingly the projections are known as Gnomonic, Orthographic or Stereographic projections

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Viewing Point

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Surface of Projection Surface of Projection can be a plane, a

cylinder or a cone Each of these surfaces can be developed into

2-Dimenionsal surface by simply unfolding or unrolling the same and without any distortion as shown in next slide

Also the aspect of map projection could be different Aspect is based on how the developable

surface is placed with respect to globe. Choice are• Normal (if axis of surface is in N-S direction)• Transverse (E-W direction)• Oblique (at an angle)

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Cylindrical Projection

Planar or Azimuthal

Conical

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Aspects of Map Projection

Normal Cylindrical

Transverse Cylindrical

Oblique Cylindrical

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Non-Perspective Projection Systems

These are based on modifying perspective projection system so that certain desired projection parameters such as shape, distance etc. are preserved.

These projections system are based on mathematical computations (Transformation equations)

Example is Mercator Projection

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What it means to you Most of GIS software allow you to choose

the projection parameters, transform data from one projection system to another.

Geographic space should be consistent for entire GIS developed A good choice could be “WGS84” When using older Survey of India toposheets or

maps, we should use “India 1975” For Projection space, “UTM” Zone 43,

North could be a good choice for Rajasthan or when using older SOI toposheets then “Lambert Conformal Conic”.

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Projection System must match

Satellite Image Projected along with vector Image

Different Projection System Satellite Data is re-projected to same Projection System