Understanding Map Projections

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GALL’S STEREOGRAPHIC Area Area is true at latitudes 45° N and S. Distortion slowly increases away from these latitudes and becomes severe at the poles. Direction Locally correct at latitudes 45° N and S. Generally distorted elsewhere. The central meridian is 176° E. DESCRIPTION Gall’s Stereographic was designed around 1855. It is a cylindrical projection with two standard parallels at latitudes 45° N and S. Distance Scale is true in all directions along latitudes 45° N and S. Scale is constant along parallels and is symmetrical around the equator. Distances are compressed between latitudes 45° N and S and expanded beyond them. LIMITATIONS Used only for world maps. USES AND APPLICATIONS Used for world maps in British atlases. PROJECTION METHOD Cylindrical stereographic projection based on two standard parallels at 45° N and S. The globe is projected perspectively onto a secant cylinder from the point on the equator opposite a given meridian. Meridians are equally spaced straight lines. Parallels are straight lines with spacing increasing away from the equator. Poles are straight lines. LINES OF CONTACT Two lines at 45° N and S. LINEAR GRATICULES All meridians and parallels. PROPERTIES Shape Shapes are true at latitudes 45° N and S. Distortion slowly increases away from these latitudes and becomes severe at the poles. 56 • Understanding Map Projections
GAUSS–KRÜGER DESCRIPTION Also known as Transverse Mercator. This projection is similar to the Mercator except that the cylinder is longitudinal along a meridian instead of the equator. The result is a conformal projection that does not maintain true directions. The central meridian is placed on the region to be highlighted. This centering minimizes distortion of all properties in that region. This projection is best suited for land masses that stretch north–south. The Gauss–Krüger (GK) coordinate system is based on the Gauss–Krüger projection. PROJECTION METHOD Cylindrical projection with central meridian placed in a particular region. LINES OF CONTACT Any single meridian for the tangent projection. For the secant projection, two parallel lines equidistant from the central meridian. LINEAR GRATICULES The equator and the central meridian. LIMITATIONS Data on a spheroid or an ellipsoid cannot be projected beyond 90 degrees from the central meridian. In fact, the extent on a spheroid or ellipsoid should be limited to 10 to 12 degrees on both sides of the central meridian. Beyond that range, data projected may not project back to the same position. Data on a sphere does not have these limitations. USES AND APPLICATIONS Gauss–Krüger coordinate system. Gauss–Krüger divides the world into zones six degrees wide. Each zone has a scale factor of 1.0 and a false easting of 500,000 meters. The central meridian of zone 1 is at 3° E. Some places also add the zone number times one million to the 500,000 false easting value. GK zone 5 could have a false easting value of 500,000 or 5,500,000 meters. The UTM system is very similar. The scale factor is 0.9996, and the central meridian of UTM zone 1 is at 177° W. The false easting value is 500,000 meters, and southern hemisphere zones also have a false northing of 10,000,000. PROPERTIES Shape Conformal. Small shapes are maintained. Shapes of larger regions are increasingly distorted away from the central meridian. Area Distortion increases with distance from the central meridian. Direction Local angles are accurate everywhere. Distance Accurate scale along the central meridian if the scale factor is 1.0. If it is less than 1.0, then there are two straight lines having an accurate scale, equidistant from and on each side of the central meridian. Supported map projections• 57
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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
Page 10 and 11:
SPHEROIDS AND SPHERES The shape and
Page 12 and 13: 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 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 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
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Eckert VI 52 ED 1950 6 Ellipse 101
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Projections (continued) planar 17,
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