Understanding Map Projections

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SPACE OBLIQUE MERCATORDESCRIPTIONThis projection is nearly conformal and has littlescale distortion within the sensing range of anorbiting mapping satellite such as Landsat. This is thefirst projection to incorporate the earth’s rotationwith respect to the orbiting satellite. For Landsat 1, 2,and 3, the path range is from 1 to 251. For Landsat 4and 5, the path range is from 1 to 233.Used to tie satellite imagery to a ground-basedplanar coordinate system and for continuousmapping of satellite imagery.Standard format used for data from Landsat 4 and 5.PROJECTION METHODModified cylindrical, for which the central line iscurved and defined by the ground track of the orbitof the satellite.LINE OF TANGENCYConceptual.LINEAR GRATICULESNone.PROPERTIESShapeShape is correct within a few parts per million forthe sensing range of the satellite.AreaVaries by less than 0.02 percent for the sensing rangeof the satellite.DirectionMinimal distortion within the sensing range.DistanceScale is true along the ground track and variesapproximately 0.01 percent within the sensing range.LIMITATIONSPlots for adjacent paths do not match withouttransformation.USES AND APPLICATIONSSpecifically designed to minimize distortion withinthe sensing range of a mapping satellite as it orbitsthe rotating earth.84 • Understanding Map Projections
STATE PLANE COORDINATE SYSTEMDESCRIPTIONAlso known as SPCS, SPC, State Plane, and State.The State Plane Coordinate System is not aprojection. It is a coordinate system that divides the50 states of the United States, Puerto Rico, and theU.S. Virgin Islands into more than 120 numberedsections, referred to as zones. Each zone has anassigned code number that defines the projectionparameters for the region.PROJECTION METHODProjection may be cylindrical or conic. See LambertConformal Conic, Transverse Mercator, and HotineOblique Mercator for methodology and properties.WHY USE STATE PLANEGovernmental organizations and groups who workwith them primarily use the State Plane CoordinateSystem. Most often, these are county or municipaldatabases. The advantage of using SPCS is that yourdata is in a common coordinate system with otherdatabases covering the same area.WHAT IS STATE PLANEThe State Plane Coordinate System was designed forlarge-scale mapping in the United States. It wasdeveloped in the 1930s by the U.S. Coast andGeodetic Survey to provide a common referencesystem to surveyors and mappers. The goal was todesign a conformal mapping system for the countrywith a maximum scale distortion of one part in10,000, then considered the limit of surveyingaccuracy.Three conformal projections were chosen: theLambert Conformal Conic for states that are longereast–west, such as Tennessee and Kentucky; theTransverse Mercator projection for states that arelonger north–south, such as Illinois and Vermont;and the Oblique Mercator projection for thepanhandle of Alaska, because it lays at an angle.To maintain an accuracy of one part in 10,000, it wasnecessary to divide many states into zones. Eachzone has its own central meridian or standardparallels to maintain the desired level of accuracy.The boundaries of these zones follow countyboundaries. Smaller states such as Connecticutrequire only one zone, while Alaska is composed of10 zones and uses all three projections.This coordinate system is referred to here as theState Plane Coordinate System of 1927 (SPCS 27). Itis based on a network of geodetic control pointsreferred to as the North American Datum of 1927(NAD 1927 or NAD27).STATE PLANE AND THE NORTH AMERICANDATUMTechnological advancements of the last 50 yearshave led to improvements in the measurement ofdistances, angles, and the earth’s size and shape.This, combined with moving the origin of the datumfrom Meades Ranch in Kansas to the earth’s center ofmass for compatibility with satellite systems, made itnecessary to redefine SPCS 27. The redefined andupdated system is called the State Plane CoordinateSystem of 1983 (SPCS 83). The coordinates for pointsare different for SPCS 27 and SPCS 83. There areseveral reasons for this. For SPCS 83, all State Planecoordinates published by NGS are in metric units,the shape of the spheroid of the earth is slightlydifferent, some states have changed the definition oftheir zones, and values of longitude and latitude areslightly changed.Officially, SPCS zones are identified by their NGScode. When ESRI ® implemented the NGS codes, theywere part of a proposed Federal InformationProcessing Standard (FIPS). For that reason, ESRIidentifies the NGS zones as FIPS zones. Thatproposed standard was withdrawn, but ESRImaintains the FIPS name for continuity.Sometimes people use an older Bureau of LandManagement (BLM) system. The BLM system isoutdated and doesn’t include codes for some of thenew zones. The values also overlap. You shouldalways use the NGS/FIPS codes.The following zone changes were made fromSPCS 27 to SPCS 83. The zone numbers listed beloware FIPS zone numbers. In addition, false easting andnorthing, or origin, of most zones has changed.California—California zone 7, SPCS 27 FIPSzone 0407, was eliminated and included in Californiazone 5, SPCS 83 FIPS zone 0405.Supported map projections• 85
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Understanding Map ProjectionsMelita
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ContentsCHAPTER 1: GEOGRAPHIC COORD
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State Plane Coordinate System .....
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GEOGRAPHIC COORDINATE SYSTEMSA geog
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SPHEROIDS AND SPHERESThe shape and
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DATUMSWhile a spheroid approximates
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2ProjectedcoordinatesystemsProjecte
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WHAT IS A MAP PROJECTION?Whether yo
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PROJECTION TYPESBecause maps are fl
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maintained for both small-scale and
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Planar projectionsPlanar projection
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OTHER PROJECTIONSThe projections di
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The four parameters above are used
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GEOGRAPHIC TRANSFORMATION METHODSMo
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Unless explicitly stated, it’s im
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National Transformation version 2Li
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LIST OF SUPPORTED MAP PROJECTIONSAi
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LoximuthalMcBryde-Thomas Flat-Polar
Page 40 and 41: AITOFFUSES AND APPLICATIONSDevelope
Page 42 and 43: ALASKA SERIES ELIMITATIONSThis proj
Page 44 and 45: AZIMUTHAL EQUIDISTANTAreaDistortion
Page 46 and 47: BIPOLAR OBLIQUE CONFORMAL CONICDESC
Page 48 and 49: CASSINI-SOLDNERAreaNo distortion al
Page 50 and 51: CRASTER PARABOLICDistanceScale is t
Page 52 and 53: DOUBLE STEREOGRAPHICOblique aspect
Page 54 and 55: ECKERT IIThe central meridian is 10
Page 56 and 57: ECKERT IVparallels. Nearer the pole
Page 58 and 59: ECKERT VIcentral meridian. Scale is
Page 60 and 61: EQUIDISTANT CYLINDRICALLINES OF CON
Page 62 and 63: GALL’S STEREOGRAPHICAreaArea is t
Page 64 and 65: GEOCENTRIC COORDINATE SYSTEMGeograp
Page 66 and 67: GNOMONICPROPERTIESShapeIncreasingly
Page 68 and 69: HAMMER-AITOFFLIMITATIONSUseful only
Page 70 and 71: KROVAKDirectionLocal angles are acc
Page 72 and 73: LAMBERT CONFORMAL CONICAreaMinimal
Page 74 and 75: LOXIMUTHALDistanceScale is true alo
Page 76 and 77: MERCATORGreenland is only one-eight
Page 78 and 79: MOLLWEIDEDistanceScale is true alon
Page 80 and 81: ORTHOGRAPHICPROPERTIESShapeMinimal
Page 82 and 83: PLATE CARRÉEDirectionNorth, south,
Page 84 and 85: POLYCONICDirectionLocal angles are
Page 86 and 87: RECTIFIED SKEWED ORTHOMORPHICDESCRI
Page 88 and 89: SIMPLE CONICEquirectangular project
Page 92 and 93: Montana—The three zones for Monta
Page 94 and 95: TIMESLIMITATIONSUseful only for wor
Page 96 and 97: 10,000,000 meters to ensure that al
Page 98 and 99: UNIVERSAL POLAR STEREOGRAPHICAreaTh
Page 100 and 101: VAN DER GRINTEN IDistanceScale alon
Page 102 and 103: WINKEL IDistanceGenerally, scale is
Page 104 and 105: WINKEL T RIPELDistanceGenerally, sc
Page 107 and 108: Glossaryangular unitsThe unit of me
Page 109 and 110: High Accuracy Reference NetworkA re
Page 111: UTMSee Universal Transverse Mercato
Page 114 and 115: Eckert VI 52ED 1950 6Ellipse 101Ell
Page 116: Projections (continued)planar 17, 1
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