Understanding Map Projections

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Conic projections The most simple conic projection is tangent to the globe along a line of latitude. This line is called the standard parallel. The meridians are projected onto the conical surface, meeting at the apex, or point, of the cone. Parallel lines of latitude are projected onto the cone as rings. The cone is then ‘cut’ along any meridian to produce the final conic projection, which has straight converging lines for meridians and concentric circular arcs for parallels. The meridian opposite the cut line becomes the central meridian. are called secant projections and are defined by two standard parallels. It is also possible to define a secant projection by one standard parallel and a scale factor. The distortion pattern for secant projections is different between the standard parallels than beyond them. Generally, a secant projection has less overall distortion than a tangent projection. On still more complex conic projections, the axis of the cone does not line up with the polar axis of the globe. These types of projections are called oblique. In general, the further you get from the standard parallel, the more distortion increases. Thus, cutting off the top of the cone produces a more accurate projection. You can accomplish this by not using the polar region of the projected data. Conic projections are used for midlatitude zones that have an east–west orientation. The representation of geographic features depends on the spacing of the parallels. When equally spaced, the projection is equidistant north–south but neither conformal nor equal area. An example of this type of projection is the Equidistant Conic projection. For small areas, the overall distortion is minimal. On Somewhat more complex conic projections contact the global surface at two locations. These projections the Lambert Conic Conformal projection, the central parallels are spaced more closely than the parallels near the border, and small geographic shapes are 14 • Understanding Map Projections
maintained for both small-scale and large-scale maps. On the Albers Equal Area Conic projection, the parallels near the northern and southern edges are closer together than the central parallels, and the projection displays equivalent areas. Projected coordinate systems • 15
Page 1 and 2: Understanding Map Projections GIS b
Page 3 and 4: Contents CHAPTER 1: GEOGRAPHIC COOR
Page 5: State Plane Coordinate System .....
Page 8 and 9: 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: PROJECTION TYPES Because maps are f
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 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
Page 114 and 115:
Eckert VI 52 ED 1950 6 Ellipse 101
Page 116:
Projections (continued) planar 17,
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