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Coordinate Systemssystems Coordinatecoordinate Systemssystems –– Keykey Conceptsconcepts CoordinateCoordinate SystemsSystems CoordinateCoordinate SystemsSystems –– keykey conceptsconcepts ►►ProjectionsProjections andand CoordinateCoordinate SystemsSystems ►►DataData QualityQuality ►►MetaMeta DataData ProjectionsProjections andand CoordinateCoordinate Systems:Systems: GeographicGeographic CoordinateCoordinate SystemSystem ►►UsesUses 3D3D sphericalspherical surfacesurface toto definedefine locationslocations ►►OftenOften incorrectlyincorrectly calledcalled aa datumdatum ►►IncludesIncludes angularangular unitunit ofof measure,measure, primeprime meridianmeridian andand datumdatum ►►PointPoint referencedreferenced byby longitude/latitudelongitude/latitude ►►AnglesAngles measuredmeasured byby degreesdegrees ParallelsParallels –– LinesLines ofof LatitudeLatitude Latitude lines are parallel The equator defines the line of zero latitude Every degree of latitude is theoretically equal Parallels run east/west; measure distances north and south of equator MeridiansMeridians –– LinesLines ofof LongitudeLongitude Meridians converge at the poles Line of zero longitude is called the Prime Meridian Distance of 1° longitude decreases toward the poles Meridians run north/south; measure distance east & west of Prime Meridian GraticularGraticular NetworkNetwork Network of Lat/Long called a graticule Origin of graticule (0,0) where Equator and Prime Meridian intersect 4 geographic quadrants based on compass bearings from Origin Degrees,Degrees, Minutes,Minutes, SecondsSeconds (DMS)(DMS) ► PointPoint onon Earth’sEarth’s surfacesurface referencedreferenced byby Lat/LongLat/Long valuesvalues ► Lat/LongLat/Long basedbased onon 360°360° ► EachEach degreedegree hashas 6060 minutesminutes ► EachEach minuteminute hashas 6060 secondsseconds DecimalDecimal DegreesDegrees (DD)(DD) ►►SimilarSimilar toto DMSDMS ►►MinutesMinutes andand secondsseconds expressedexpressed asas decimaldecimal valuesvalues ►►ESRIESRI productsproducts requirerequire DDDD inin geodatasetsgeodatasets ConvertingConverting fromfrom DMSDMS toto DDDD 37°37° 36'36' 30"30" (DMS)(DMS) ►►DivideDivide eacheach valuevalue byby thethe numbernumber ofof minutesminutes oror secondsseconds inin aa degree:degree: 3636 minutesminutes == .60.60 degreesdegrees (36/60)(36/60) 3030 secondsseconds == .00833.00833 degreesdegrees (30/3600)(30/3600) ►► AddAdd upup thethe degreesdegrees toto getget thethe answer:answer: ►►37°37° ++ .60°.60° ++ .00833°.00833° == 37.6083337.60833 DDDD SpheresSpheres andand SpheroidsSpheroids Sphere Spheroid •Shape and size of GCS surface defined by sphere or spheroid. •Mathematical calculations easier on a sphere. •Sphere can be used for small-scale maps (< 1:5,000,000) •Spheroid gives better accuracy for large-scale maps (>1:1,000,000 MajorMajor andand MinorMinor AxesAxes ofof EllipseEllipse Minor Axis Major Axis Semiminor Axis Semimajor Axis Shape of ellipse defined by two radii. Longer radius: Semimajor Axis Shorter radius: Semiminor Axis Rotating spheroid around semiminor axis creates a spheroid SpheroidsSpheroids forfor AccurateAccurate MappingMapping ► EarthEarth hashas beenbeen surveyedsurveyed manymany timestimes ► SurveysSurveys resultresult inin manymany spheroidsspheroids ► SpheroidSpheroid chosenchosen toto fitfit oneone countrycountry ► BestBest fitfit forfor oneone regionsregions notnot samesame forfor anotheranother regionregion ► EarthEarth isis neitherneither perfectperfect spheresphere nornor spheroidspheroid ► ChangingChanging coordinatecoordinate system’ssystem’s spheroidspheroid changeschanges allall previouslypreviously measuredmeasured valuesvalues DatumsDatums ►►SpheroidsSpheroids approximateapproximate earth’searth’s shapeshape ►►DatumDatum definesdefines positionposition ofof spheroidspheroid relativerelative toto centercenter ofof thethe earthearth ►►DatumDatum definesdefines originorigin andand orientationorientation ofof lat/longlat/long lineslines ►►LocalLocal datumdatum alignsaligns spheroidspheroid toto fitfit surfacesurface inin aa particularparticular areaarea DatumDatum ComparisonsComparisons Local geographic Coordinate system Earth-centered geographic Coordinate system Earth’s surface Earth-centered datum Local datum NorthNorth AmericanAmerican DatumsDatums ► NAD27NAD27 –– uses Clarke 1866 spheroid Origin – Meade Ranch Kansas Manually calculated control points ► NAD83NAD83 Based on earth and satellite observations Uses GRS80 spheroid Origin is earth’s center of mass Previous control points shift as much as 500’ ProjectedProjected CoordinateCoordinate SystemsSystems ►►DefinedDefined onon flat,flat, 2D2D surfacesurface ►►HasHas constantconstant lengths,lengths, anglesangles andand areaarea ►►AlwaysAlways basedbased onon geographicgeographic coordinatecoordinate systemsystem ►►X,YX,Y coordinatescoordinates onon gridgrid WhatWhat isis aa MapMap Projection?Projection? ► TransformationTransformation ofof 3D3D surfacesurface toto 2D2D flatflat sheetsheet ► CausesCauses distortiondistortion inin thethe shape,shape, area,area, distancedistance oror directiondirection ofof datadata ► UsesUses mathematicalmathematical formulasformulas toto relaterelate sphericalspherical coordinatescoordinates toto planarplanar coordinatescoordinates ► DifferentDifferent projectionsprojections causecause differentdifferent distortionsdistortions ► MapMap projectionsprojections designeddesigned forfor specificspecific purposepurpose –– i.e.i.e. largelarge--scalescale datadata inin limitedlimited areaarea RelevanceRelevance toto GISGIS ► mapsmaps areare aa commoncommon sourcesource ofof inputinput datadata forfor aa GISGIS 1) often input maps will be in different projections, requiring transformation of one or all maps to make coordinates compatible 2) thus, mathematical functions of projections are needed in a GIS ► oftenoften GISGIS areare usedused forfor projectsprojects ofof globalglobal oror regionalregional scalesscales soso considerationconsideration ofof thethe effecteffect ofof thethe earth'searth's curvaturecurvature isis necessarynecessary ► monitormonitor screensscreens areare analogousanalogous toto aa flatflat sheetsheet ofof paperpaper 1) thus,thus, needneed toto provideprovide transformationstransformations fromfrom thethe curvedcurved surfacesurface toto thethe planeplane forfor displayingdisplaying datadata ConclusionConclusion ►►WhatWhat isis aa coordinatecoordinate system?system? AA coordinatecoordinate systemsystem isis aa gridgrid thatthat maymay bebe usedused toto definedefine wherewhere aa particularparticular locationlocation isis ►►ConnectionConnection betweenbetween projectionprojection andand coordinatecoordinate systemsystem TheThe projectionprojection definesdefines thethe coordinatecoordinate systemsystem byby definingdefining thethe 22--DD surfacesurface ofof thethe earthearth.
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