Understanding Map Projections

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GNOMONIC PROPERTIES Shape Increasingly distorted from the center; moderate distortion within 30 degrees of the center point. Area Distortion increases with distance from the center; moderate distortion within a 30 degree radius of the center. Direction Accurate from the center. Distance No line has an accurate scale, and the amount of distortion increases with distance from the center. The central meridian is 0°, and the latitude of origin is 90° S. DESCRIPTION This azimuthal projection uses the center of the earth as its perspective point. All great circles are straight lines, regardless of the aspect. This is a useful projection for navigation because great circles highlight routes with the shortest distance. PROJECTION METHOD This is a planar perspective projection viewed from the center of the globe. The projection can be any aspect. POINT OF TANGENCY A single point anywhere on the globe. Polar aspect—North Pole or South Pole. Equatorial aspect—Any point along the equator. Oblique aspect—Any other point. LINEAR GRATICULES All meridians and the equator. Scalar Distortion for Polar Aspect Degrees from Center (°) 15.0 30.0 45.0 60.0 Meridian Distortion (%) 7.2 33.3 100.0 300.0 Latitude Distortion (%) 3.5 15.5 41.4 100.0 LIMITATIONS This projection is limited by its perspective point and cannot project a line that is 90 degrees or more from the center point; this means that the equatorial aspect cannot project the poles and the polar aspects cannot project the equator. A radius of 30 degrees produces moderate distortion, as indicated in the table above. This projection should not be used more than about 60 degrees from the center. USES AND APPLICATIONS All aspects—Routes of navigation for sea and air. Polar aspect—Navigational maps of polar regions. Equatorial aspect—Navigational maps of Africa and the tropical region of South America. 60 • Understanding Map Projections
GREAT BRITAIN NATIONAL GRID Direction Local directions are accurately maintained. Distance Scale is accurate along the lines of secancy 180 km from the central meridian. Scale is compressed between them and expanded beyond them. LIMITATIONS Suitable for Great Britain. Limited in east–west extent. USES AND APPLICATIONS The national coordinate system for Great Britain; used for large-scale topographic mapping. The central meridian is 2° W, and the latitude of origin is 49° N. The scale factor is 0.9996. DESCRIPTION This is a Transverse Mercator projected on the Airy spheroid. The central meridian is scaled to 0.9996. The origin is 49° N and 2° W. PROJECTION METHOD Cylindrical, transverse projection with the central meridian centered along a particular region. LINES OF CONTACT Two lines parallel with and 180 km from the central meridian at 2° W. LINEAR GRATICULES The central meridian. PROPERTIES Shape Conformal; therefore, small shapes are maintained accurately. Area Distortion increases beyond Great Britain as the distance from the central meridian increases. Supported map projections• 61
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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
Page 15 and 16: 2 Projected coordinate systems Proj
Page 17 and 18: WHAT IS A MAP PROJECTION? Whether y
Page 19 and 20: PROJECTION TYPES Because maps are f
Page 21 and 22: maintained for both small-scale and
Page 23 and 24: Planar projections Planar projectio
Page 25 and 26: OTHER PROJECTIONS The projections d
Page 27: The four parameters above are used
Page 30 and 31: GEOGRAPHIC TRANSFORMATION METHODS M
Page 32 and 33: Unless explicitly stated, it’s im
Page 34 and 35: National Transformation version 2 L
Page 36 and 37: LIST OF SUPPORTED MAP PROJECTIONS A
Page 38 and 39: Loximuthal McBryde-Thomas Flat-Pola
Page 40 and 41: 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 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 92 and 93: Montana—The three zones for Monta
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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