Geog 458: Map Sources and ErrorOutlinesPlacenamesPostal addressesLinear referencingGeodetic modelUnprojected coordinate systemProjected coordinate systemGrid coordinate systemsMetadata Content Standard: Section 4: Spatial ReferenceReading metadata content standardExerciseGeog 458:Geog 458:Map Sources and Map Sources and ErrorErrorJanuary 18, 2006January 18, 2006GeoreferencingGeoreferencingOutlinesOutlinesPlacenamesPlacenamesPostal addressesPostal addressesMetric georeferencingMetric georeferencing1D: Linear referencing systems1D: Linear referencing systems3D: Unprojected coordinate system3D: Unprojected coordinate systemGeodetic modelGeodetic model2D: Projected coordinate system2D: Projected coordinate systemMMap projection: how it worksap projection: how it worksGrid coordinate systems: UTM, SPCGrid coordinate systems: UTM, SPCMetadata content standard: spatial reference Metadata content standard: spatial referencePlacenamesPlacenamesSimplest form of georeferencingSimplest form of georeferencingWWhere do you live? I live in university districthere do you live? I live in university districtLimited use in GIS due to imprecise location; Limited use in GIS due to imprecise location; meaning of placenamesmeaning of placenamescan vary between people, and with contextcan vary between people, and with contextcan be uniquely identified with proper geographic can be uniquely identified with proper geographic hierarchyhierarchycan change over timecan change over timeTo be used in GIS or other applications, it is To be used in GIS or other applications, it is necessary to systematically identify precise necessary to systematically identify precise location of names of geographic featureslocation of names of geographic featuresGNIS (Geographic Names Information System)GNIS (Geographic Names Information System)In the website, find out wIn the website, find out what it is, how it works, and hat it is, how it works, and purposespurposesPostal addressesPostal addressesWidely used to identify the location of dwellingsWidely used to identify the location of dwellingsBased on several assumptionsBased on several assumptionsLocal areas are identified with proper geographic Local areas are identified with proper geographic hierarchy hierarchy Path is unique within local areasPath is unique within local areasDwellings are numbered consecutively along the pathDwellings are numbered consecutively along the pathHow does address-matching work?How does address-matching work?Look at TIGER/Line road dataLook at TIGER/Line road dataLinear interpolation based on topologic dataLinear interpolation based on topologic dataAAny limitation?ny limitation?Linear referencingLinear referencingIIdentify location on a network by dentify location on a network by measuring distance from a defined point measuring distance from a defined point of reference along a defined path in the of reference along a defined path in the networknetwork1-dimensional: stored in a tabular form1-dimensional: stored in a tabular formWidely used in highway agency (DOT): Widely used in highway agency (DOT): vary by State, reference point is split vary by State, reference point is split along administrative boundaryalong administrative boundaryLLook at NHPN dataook at NHPN dataGeodetic modelGeodetic modelTo determine the location precisely, it is To determine the location precisely, it is necessary to define the shape of earthnecessary to define the shape of earthEarth is not quite spherical, but rather ellipsoidEarth is not quite spherical, but rather ellipsoidEllipsoid (a.k.a. spheroid): geodetic model of the Ellipsoid (a.k.a. spheroid): geodetic model of the earthearthFlattening ratio defines how the model differs from Flattening ratio defines how the model differs from spheresphereDifferent ellipsoid has different flattening ratioDifferent ellipsoid has different flattening ratioEllipsoid can be either earth-centered (global) or Ellipsoid can be either earth-centered (global) or not (local), arising from the need to approximate not (local), arising from the need to approximate the shape of the earth suited to varying coverage the shape of the earth suited to varying coverage areasareasNAD29 is local datumNAD29 is local datumWGS84 is global datumWGS84 is global datumUnprojected coordinate Unprojected coordinate systemsystem3 dimensional 3 dimensional Latitude: angle from the equatorLatitude: angle from the equatorLongitude: offset from prime meridianLongitude: offset from prime meridianGeographic unit of measurement Geographic unit of measurement Decimal degrees = degree + minute /60 + second Decimal degrees = degree + minute /60 + second / 3600/ 3600OOthther nameser namesGeographicGeographic system of coordinates system of coordinatesPlate CarreePlate CarreeSince it’s unprojected, it gives a heavily Since it’s unprojected, it gives a heavily distorted image of the earth (e.g. Antarctica)distorted image of the earth (e.g. Antarctica)Projected coordinate Projected coordinate systemsystem2-dimensional; involves map projection 2-dimensional; involves map projection (transformation of 3D to 2D); a.k.a. (transformation of 3D to 2D); a.k.a. planarplanar coordinate systemcoordinate systemPProjection family (the shape of developable surface)rojection family (the shape of developable surface)CCylindrical, conic, planarylindrical, conic, planarProjection properties (which geometric property is Projection properties (which geometric property is constant?)constant?)Equal-area, conformal, equidistance, azimuthalEqual-area, conformal, equidistance, azimuthalTangency: Tangent, secantTangency: Tangent, secantAspect: Normal, transverse, obliqueAspect: Normal, transverse, obliqueStandard line or standard parallelStandard line or standard parallelWhere earth intersects developable surfaceWhere earth intersects developable surfaceLLine of zero distortionine of zero distortionGrid coordinate systemsGrid coordinate systemsUTMUTMUniversal Transverse MercatorUniversal Transverse MercatorProjection family?Projection family?Projection property?Projection property?Tangency?Tangency?Aspect?Aspect?1 zone is ? degree1 zone is ? degreeSPCSPCState by stateState by stateUUse three different map projections depending on se three different map projections depending on