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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
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