GIS MAP PROJECTIONS

Muhammd Bilal SaleemSession 2012-2014M.Phil Geomatics

DESCRIPTION

Two dimensional representation of the three dimensional Earth Systematic transformation of latitudes and longitudes to parallels

and meridians respectively An intriguing component of the coordinate system referencing

because it portrays high level of flexibility Transformation cause distortion in real world properties that are:1. Shape2. Area3. Distance4. Direction

DEVELOPABLE PROJECTION SURFACES

Determine specific method of physical projection Three kinds of developable projection surfaces:1. Cone2. Cylinder3. Plane The name of the projections made from these surface are:1. Conic Projection2. Cylindrical Projection3. Planar Projection

1. Conic Projection: Conic projection is fan shaped,

characterized by an upside down cone over the sphere

Conic projection are at an true scale along a standard parallel/s between the equator and a pole

Conic projections are used for midlatitude zones that have an east–west orientation

If equally space, distance preserve If distance between parallels increase

near border, shape preserve If distance towards north and south

pole decreases, area preserve

2. Cylindrical Projection: Cylindrical projection is a rectangular

grid representation, characterized by a cylinder over a sphere

Cylindrical projections are at an true scale along a central meridian/s and standard parallel/s near a equator

Cylindrical projection mostly use for tropical zones

All cylindrical projections are equidistant along central meridian/s and standard parallel/s

3. Planar Projection: Planar projection is a circular

representation with a focus, characterized by plane over a sphere

Planar projection is also called Azimuthal projection or Zenithal projection

Planar projections are true only at their focus

Planar projections mostly use for polar zones

Planar projection more better describe circular regions than rectangular regions

Azimuthal Projection is further divided into three different projection on the basis of projection focus:

1. Gnomonic/ Central projection2. Stereographic Projection3. Orthographic Projection1) Gnomonic Projection:

Azimuthal projection in which projection focus is at center of the Earth

2) Stereographic Projection:Azimuthal projection in which projection focus is from pole to pole

3) Orthographic Projection:Azimuthal projection in which projection focus is at infinity

LOCATION OF DEVELOPABLE PROJECTION SURFACE

There are two cases in which developable projection surface meet Earth:

1. Tangent: DPS touches the EarthOne standard parallel/ One Central meridian

2. Secant:DPS cuts the EarthTwo standard parallels/ Two central meridians

ASPECT OF DEVELOPABLE PROJECTION SURFACE

Projection aspect is the relative orientation of the developable projection surface and Earth with respect to the observer

There are four kinds of projection aspects:1. Normal2. Transverse3. Oblique4. Polar

1) Normal Aspect: Oriented with polar axis Based on parallels Normal aspect is Equatorial aspect if

standard parallel is equator Normal aspect is Azimuthal aspect if

standard parallel touches poles

2) Transverse Aspect: Oriented perpendicular to polar axis Based on meridians

3) Oblique Aspect: Oriented at any angle with polar axis Based on central meridian and

standard parallel Use for geographical areas that are

centered along lines that are neither parallel nor meridians

Directed as northwest, northeast, southwest and southeast

4) Polar Aspect: Oriented on focus as north or

south pole Based on straight meridians

with a concentric parallels Polar aspect only related to

planar projection or Azimuthal projection or Zenithal projection

PROJECTION CLASSIFICATIONS Classification defines a properties of the projected surfaces The names of the properties that preserves by the projected surfaces are

given below:1. Shape: Conformal or Orthomorphic2. Area: Equal Area or Equivalent3. Distance: Equidistant4. Direction: Azimuthal

1) Conformal Projection: Preserve shapes of small regions of the Earth that’s why use for medium

scale to large scale applications Shape preserve either angle preserve or scale preserve No projection preserve shape of larger regions Can preserve Direction by maintaining an angle between graticule lines Area of the region distorted for large scale applications

2) Equal Area or Equivalent: Preserve area of all regions of the Earth’s surface that’s why use for

small scale to large scale applications Area preserve when scale vary equally on both sided of the standard

parallel Area and shape cannot preserve simultaneously For small scale applications, Direction also distorted

3) Equidistant: Preserve distance between entire regions of the Earth that are at true

scale that’s why use for small scale to large scale applications Distance only preserve when scale preserve No projection is equidistant to and from all points on a map

4) Azimuthal: Preserve direction of all regions of the Earth that’s why use for medium to

large scale applications Direction preserve when angle preserve Azimuthal projection can be equal area, conformal or equidistant

Formation of Map Projections: DPS can exhibit more than one classification The conic projection, cylindrical projection and planar projection can be

combined with one or more of the projection classifications to control the appearance and distortion for any particular application

There are lot of projections that can made by this procedure. Some of the projections will discussed

MERCATOR PROJECTION Cylindrical projection Normal aspect Equator/ Two latitudes symmetrical

around the equator Meridians are parallel to each other

and equally spaced Parallels are parallel but become

farther apart toward the poles Distance preserve along Equator or

Two latitudes Shape preserve accurately Direction preserve accurately along

graticule lines Area not preserved and increase

towards the top and bottom of the map Use in Standard sea navigation charts,

Wind direction, Air travel and Ocean currents

Application in Conformal world maps

CYLINDRICAL EQUAL AREA PROJECTION Cylindrical projection Equatorial aspect Tangent to the equator All meridians are equally spaced and

0.32 times the length of the equator Parallels are equally spaced and

farthest apart near the equator Poles are lines of length equal to the

equator Distance preserve along equator Shape not preserve because of scale

variation Direction not preserved but local angle

preserve along standard parallels Area preserve accurately Use for narrow areas extending along

the equatorial regions

UNIVERSAL TRANSVERSE MERCATOR PROJECTION Cylindrical projection Transverse aspect Two parallel lines spaced from each

central meridian by 180 km Earth is divided into 60 zones that

are spanning 6⁰ of longitude form 84⁰N & 80⁰S with central meridian of each zone and equator

Distance preserve along each central meridian

Shape not preserve accurately Direction preserve for each zone Area preserved and minimal

distortion along the boundary of zone Extent should be limited to 15⁰-20 ⁰

on both sides of the central meridian Many countries use local UTM zones

based on the official geographic coordinate systems in use

EQUIDISTANT CONIC PROJECTION Conical Projection Normal aspect Tangential/ Secant Concentric circles of parallels and all

meridians are evenly spaced Distance preserve accurately along

meridians and standard parallels Shape preserve along standard parallels Direction not preserve but local angle

preserve Area not preserved and increases as

moving away from standard parallels Range in parallels should be limited to

30° Use for Regional mapping of

midlatitude areas with a predominantly east–west extent

Application in Atlas maps of small countries

ALBERS EQUAL AREA PROJECTION Conic projection Normal aspect Secant All meridians equally spaced Distance between concentric

parallels decreases toward poles Distance preserve for mid latitude Shape not preserve and distortion

increases between standard parallels Direction not preserve but local

angle preserve Area preserve accurately Used for small countries but not for

continents. Used for the conterminous United

States

LAMBERT CONFORMAL CONICAL PROJECTION

Conic projection Normal aspect Secant All meridians are equally spaced Distance between arc of parallels

increases near a border Distance preserve for mid latitude Shape preserve accurately Direction preserve accurately Area not preserved except small

regions near standard parallels All latitudinal range should not

exceed 35° Use for regions that have east-

west extension

LAMBERT AZIMUTHAL EQUAL AREA PROJECTION

Planar projection Equatorial, polar and oblique aspect Tangent of single pint anywhere Equatorial aspect: The equator Polar aspect: All meridians Oblique aspect: Central meridian Distance preserve only along focus Shape not preserved because of about 2%

error within 15° from focus Direction preserve accurately from focus Area preserve accurately Use for Population density, Political

boundaries Use in Oceanic mapping for energy,

Minerals, Geology, and Tectonics

Use for displaying entire continents Equatorial aspect: Africa, Southeast Asia, Australia,

the Caribbean, and Central America Polar aspect: Polar regions Oblique aspect: North America, Europe, and Asia

UNIVERSAL POLAR STEREOGRAPHIC PROJECTION

Stereographic projection Polar aspect Tangent at pole The focus is either a north pole or south pole

to 84° N and 80° S The latitude 81°06'52.3" N or 81°06'52.3" S

at true scale and all meridians Distance preserve only at focus and latitude

of 81°06'52.3" N or 81°06'52.3" S Shape preserve accurately Direction preserve accurately from focus Area not preserve and increases moving

away from focus Use for Conformal mapping of polar regions Use for mapping polar regions of the UTM

coordinate system

OTHERS PROJECTIONS The other projections which are not conceptually made and not

easily related to developable projection surface There are three kinds of these projections:1. Modified projection2. Pseudo projection3. Compromise projection

1) Modified Projection: Modified form of conceptual projections to reduce distortion For example, the Space Oblique Mercator projection is a

modified form of Mercator projection, Aitoff is a modified form of planar projection etc

2) Pseudo Projection: Have some Characteristics of another class of projection For example, the Sinusoidal is called a pseudo cylindrical

projection, Bonne is called pseudo conic projection and Werner is called pseudo planar projection etc

3) Compromise Projection: Average or interrupted form of different projection For example, Goode's Homolosine projection is a combination

of the Mollweide and sinusoidal projections etc