Understanding Map Projections

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Montana—The three zones for Montana, SPCS 27 FIPS zones 2501, 2502, and 2503, were eliminated and replaced by a single zone, SPCS 83 FIPS zone 2500. Nebraska—The two zones for Nebraska, SPCS 27 FIPS zones 2601 and 2602, were eliminated and replaced by a single zone, SPCS 83 FIPS zone 2600. USES AND APPLICATIONS Used for standard USGS 7½- and 15-minute quad sheets. Used for most federal, state, and local large-scale mapping projects in the United States. South Carolina—The two zones for South Carolina, SPCS 27 FIPS zones 3901 and 3902, were eliminated and replaced by a single zone, SPCS 83 FIPS zone 3900. Puerto Rico and Virgin Islands—The two zones for Puerto Rico and the Virgin Islands, St. Thomas, St. John, and St. Croix, SPCS 27 FIPS zones 5201 and 5202, were eliminated and replaced by a single zone, SPCS 83 FIPS zone 5200. UNIT OF LENGTH The standard unit of measure for SPCS 27 is the U.S. Survey foot. For SPCS 83, the most common unit of measure is the meter. Those states that support both feet and meters have legislated which feet-to-meters conversion they use. The difference between the two is only two parts in one million, but that can become noticeable when datasets are stored in double precision. The U.S. Survey foot equals 1,200/3,937 m, or 0.3048006096 m. EXAMPLES OF ZONE DEFINITIONS Here are two examples of SPCS 83 parameters: State Alabama East Tennessee ZONE 3101 5301 FIPS Zone 0101 4100 Projection Transverse Lambert Standard Parallels 35°15' 36°25' Central Meridian -85°50' -86°00' Scale Factor Reduction at Central Meridian 1:25,000 1:15,000 Latitude of Origin 30°30' 34°20' Longitude of Origin -85°50' -86°00' False Easting 200,000 600,000 False Northing 0 0 86 •Understanding Map Projections
STEREOGRAPHIC PROPERTIES Shape Conformal. Local shapes are accurate. Area True scale at center with distortion increasing with distance. Direction Directions are accurate from the center. Local angles are accurate everywhere. Distance Scale increases with distance from the center. The central meridian is 0°, and the latitude of origin is 90° S. DESCRIPTION This projection is conformal. PROJECTION METHOD Planar perspective projection, viewed from the point on the globe opposite the point of tangency. Stereographic projects points on a spheroid directly to the plane. See Double Stereographic for a different implementation. LIMITATIONS Normally limited to one hemisphere. Portions of the outer hemisphere may be shown, but with rapidly increasing distortion. USES AND APPLICATIONS The oblique aspect has been used to map circular regions on the moon, Mars, and Mercury. All meridians and parallels are shown as circular arcs or straight lines. Graticular intersections are 90 degrees. In the equatorial aspect, the parallels curve in opposite directions on either side of the equator. In the oblique case, only the parallel with the opposite sign to the central latitude is a straight line; other parallels are concave toward the poles on either side of the straight parallel. POINT OF CONTACT A single point anywhere on the globe. LINEAR GRATICULES Polar aspect—All meridians. Equatorial aspect—The central meridian and the equator. Oblique aspect—Central meridian and parallel of latitude with the opposite sign of the central latitude. Supported map projections• 87
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Understanding Map Projections GIS b
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Contents CHAPTER 1: GEOGRAPHIC COOR
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State Plane Coordinate System .....
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GEOGRAPHIC COORDINATE SYSTEMS A geo
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SPHEROIDS AND SPHERES The shape and
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DATUMS While a spheroid approximate
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2 Projected coordinate systems Proj
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WHAT IS A MAP PROJECTION? Whether y
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PROJECTION TYPES Because maps are f
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maintained for both small-scale and
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Planar projections Planar projectio
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OTHER PROJECTIONS The projections d
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The four parameters above are used
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GEOGRAPHIC TRANSFORMATION METHODS M
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Unless explicitly stated, it’s im
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National Transformation version 2 L
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LIST OF SUPPORTED MAP PROJECTIONS A
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Loximuthal McBryde-Thomas Flat-Pola
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AITOFF USES AND APPLICATIONS Develo
Page 42 and 43: ALASKA SERIES E LIMITATIONS This pr
Page 44 and 45: AZIMUTHAL EQUIDISTANT Area Distorti
Page 46 and 47: BIPOLAR OBLIQUE CONFORMAL CONIC DES
Page 48 and 49: CASSINI-SOLDNER Area No distortion
Page 50 and 51: CRASTER PARABOLIC Distance Scale is
Page 52 and 53: DOUBLE STEREOGRAPHIC Oblique aspect
Page 54 and 55: ECKERT II The central meridian is 1
Page 56 and 57: ECKERT IV parallels. Nearer the pol
Page 58 and 59: ECKERT VI central meridian. Scale i
Page 60 and 61: EQUIDISTANT CYLINDRICAL LINES OF CO
Page 62 and 63: GALL’S STEREOGRAPHIC Area Area is
Page 64 and 65: GEOCENTRIC COORDINATE SYSTEM Geogra
Page 66 and 67: GNOMONIC PROPERTIES Shape Increasin
Page 68 and 69: HAMMER-AITOFF LIMITATIONS Useful on
Page 70 and 71: KROVAK Direction Local angles are a
Page 72 and 73: LAMBERT CONFORMAL CONIC Area Minima
Page 74 and 75: LOXIMUTHAL Distance Scale is true a
Page 76 and 77: MERCATOR Greenland is only one-eigh
Page 78 and 79: MOLLWEIDE Distance Scale is true al
Page 80 and 81: ORTHOGRAPHIC PROPERTIES Shape Minim
Page 82 and 83: PLATE CARRÉE Direction North, sout
Page 84 and 85: POLYCONIC Direction Local angles ar
Page 86 and 87: RECTIFIED SKEWED ORTHOMORPHIC DESCR
Page 88 and 89: SIMPLE CONIC Equirectangular projec
Page 90 and 91: SPACE OBLIQUE MERCATOR DESCRIPTION
Page 94 and 95: TIMES LIMITATIONS Useful only for w
Page 96 and 97: 10,000,000 meters to ensure that al
Page 98 and 99: UNIVERSAL POLAR STEREOGRAPHIC Area
Page 100 and 101: VAN DER GRINTEN I Distance Scale al
Page 102 and 103: WINKEL I Distance Generally, scale
Page 104 and 105: WINKEL T RIPEL Distance Generally,
Page 107 and 108: Glossary angular units The unit of
Page 109 and 110: High Accuracy Reference Network A r
Page 111: UTM See Universal Transverse Mercat
Page 114 and 115: Eckert VI 52 ED 1950 6 Ellipse 101
Page 116: Projections (continued) planar 17,
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