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Map Projection. - PowerPoint PPT Presentation
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Map ProjectionMap ProjectionA map projection is a A map projection is a set of rulesset of rules for for transforming featurestransforming features from the from the
threethree-dimensional earth onto a -dimensional earth onto a twotwo-dimensional display. No flat -dimensional display. No flat representation of the earth can be completely accurate, so many representation of the earth can be completely accurate, so many different projections have been developed, each suited to a different projections have been developed, each suited to a particular purpose. Map projections differ in the way they handle particular purpose. Map projections differ in the way they handle four propertiesfour properties::
AreaArea, , AnglesAngles, , DistanceDistance and and DirectionDirection. .
Rules:Rules:
1.1. No projection can preserve all four simultaneously, although some combinations No projection can preserve all four simultaneously, although some combinations can be preserved, such ascan be preserved, such as AreaArea and and DirectionDirection
2.2. No projection can preserve both No projection can preserve both AreaArea and and AnglesAngles, however. The map-maker, however. The map-maker must decide which property is must decide which property is most importantmost important and choose a projection and choose a projection based on based on
that.that.
http://mac.usgs.gov/mac/isb/pubs/MapProjections/projections.htmlLearn more:
Reza Wahadj
Presented by
Concept of Geoprocessing and Projections
Projections and CoordinatesProjections and Coordinates
There are many reasons for wanting to There are many reasons for wanting to project the Earth’s surface onto a plane, project the Earth’s surface onto a plane, rather than deal with the curved surfacerather than deal with the curved surface The paper used to output GIS maps is flatThe paper used to output GIS maps is flat Flat maps are scanned and digitized to create GIS Flat maps are scanned and digitized to create GIS
databasesdatabases Rasters are flat, it’s impossible to create a raster Rasters are flat, it’s impossible to create a raster
on a curved surfaceon a curved surface The Earth has to be projected to see all of it at The Earth has to be projected to see all of it at
onceonce It’s much easier to measure distance on a planeIt’s much easier to measure distance on a plane
Coordinate SystemsCoordinate Systems
Spatial data are referenced to locations on the earth’s Spatial data are referenced to locations on the earth’s surface using coordinate systemssurface using coordinate systems Ensure all map layers share a common coordinate systemEnsure all map layers share a common coordinate system
Recognized global coordinate systems consist of:Recognized global coordinate systems consist of: A Spheroid: a mathematical description of the earth’s shapeA Spheroid: a mathematical description of the earth’s shape A Map Projection: a mathematical conversion from spherical A Map Projection: a mathematical conversion from spherical
to planar coordinatesto planar coordinates
Map ProjectionMap Projection
Normal or Polar Oblique Transverse orEquatorial
Different View
Normal or Polar ObliqueTransverse or
Equatorial
Different View
Different familyDifferent family
coniccylindricalazimuthal
Projection different familyProjection different family
coniccylindricalazimuthal
Distortion patterns
Direction of Distortion Direction of Distortion
Transverse MercatorTransverse Mercator
Projection propertiesProjection properties Conformal cylindricalConformal cylindrical Rhumb lines Rhumb lines notnot projected as straight lines projected as straight lines Transverse -- standard line is a meridianTransverse -- standard line is a meridian
Projection usesProjection uses Topographic maps (USGS)Topographic maps (USGS) As a base for the UTM coordinate systemAs a base for the UTM coordinate system As a base for state plane coordinatesAs a base for state plane coordinates
conformal distancedirectionequal area
Universal Transverse Universal Transverse Mercator (UTM)Mercator (UTM)
Projection propertiesProjection properties All Transverse propertiesAll Transverse properties Standard line is a meridianStandard line is a meridian 60 zone divided 60 zone divided
Projection usesProjection uses World MapWorld Map
conformal distancedirectionequal area
conformal distancedirectionequal area
Azimuthal Equidistant
Projection properties• Distances are correct outward from center• Possible to show the entire sphere
Projection uses• Sea and air navigation planning• Distance from a specified location to all
others
conformal distancedirectionequal area
Robinson
Projection properties• Compromise
Projection uses• World atlas maps
Uses tabular coordinates rather than mathematical formulasto make the world "look right."
Directions true along all parallels and along central meridian
Distances constant along Equator and other parallels
GeoreferencingGeoreferencing
Is essential in GIS, since all information must Is essential in GIS, since all information must be linked to the Earth’s surfacebe linked to the Earth’s surface
The method of georeferencing must be:The method of georeferencing must be: Unique, linking information to exactly one locationUnique, linking information to exactly one location Shared, so different users understand the Shared, so different users understand the
meaning of a georeferencemeaning of a georeference Persistent through time, so today’s georeferences Persistent through time, so today’s georeferences
are still meaningful tomorroware still meaningful tomorrow
Georeferences as MeasurementsGeoreferences as Measurements
Some georeferences are metricSome georeferences are metric They define location using measures of distance They define location using measures of distance
from fixed placesfrom fixed places E.g., distance from the Equator or from the Greenwich E.g., distance from the Equator or from the Greenwich
MeridianMeridian
Others are based on orderingOthers are based on ordering E.g. street addresses in most parts of the world E.g. street addresses in most parts of the world
order houses along streetsorder houses along streets Others are only nominalOthers are only nominal
Placenames do not involve ordering or measuringPlacenames do not involve ordering or measuring
PlacenamesPlacenames
The earliest form of georeferencingThe earliest form of georeferencing And the most commonly used in everyday activitiesAnd the most commonly used in everyday activities
Many names of geographic features are Many names of geographic features are universally recognizeduniversally recognized Others may be understood only by localsOthers may be understood only by locals
Names work at many different scalesNames work at many different scales From continents to small villages and neighborhoodsFrom continents to small villages and neighborhoods
Names may pass out of use in timeNames may pass out of use in time
ZIP code boundaries are a convenient way to summarize data in the US. The dots on the left have been summarized as a density per square
mile on the right
Linear ReferencingLinear Referencing
A system for A system for georeferencing positions georeferencing positions on a road, street, rail, or on a road, street, rail, or river networkriver network
Combines the name of Combines the name of the link with an offset the link with an offset distance along the link distance along the link from a fixed point, most from a fixed point, most often an intersectionoften an intersection
Users of Linear ReferencingUsers of Linear Referencing
Transportation authoritiesTransportation authorities To keep track of pavement quality, signs, To keep track of pavement quality, signs,
traffic conditions on roadstraffic conditions on roads PolicePolice
To record the locations of accidentsTo record the locations of accidents
Converting GeoreferencesConverting Georeferences
GIS applications often require conversion of GIS applications often require conversion of projections and ellipsoidsprojections and ellipsoids These are standard functions in popular GIS These are standard functions in popular GIS
packagespackages
Street addresses must be converted to Street addresses must be converted to coordinates for mapping and analysiscoordinates for mapping and analysis Using Using geocodinggeocoding functions functions
Placenames can be converted to coordinates Placenames can be converted to coordinates using using gazetteersgazetteers
Geographic Information ViewerGeographic Information Viewer
EasyEasy LightweightLightweight
New System for Publishing MapsNew System for Publishing Maps
ArcReader is ViewerArcReader is Viewer
ArcGIS isArcGIS isAuthor/PublisherAuthor/Publisher
Map DocMap Doc
ArcGISArcGIS DataData
ArcReaderArcReader
ArcReaderArcReader
A New ExtensionA New Extension
PublisherPublisher
ArcMapArcMap
DataDataMXDMXD
PMFPMF
Publisher Authors Publisher Authors PMF DocumentsPMF Documents