Understanding Map Projections

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ALASKA SERIES E LIMITATIONS This projection is appropriate for mapping Alaska, the Aleutian Islands, and the Bering Sea region only. USES AND APPLICATIONS 1972 USGS revision of a 1954 Alaska map that was published at 1:2,500,000 scale. 1974 map of the Aleutian Islands and the Bering Sea. Parameters are set by the software. DESCRIPTION This projection was developed in 1972 by the USGS to publish a map of Alaska at 1:2,500,000 scale. PROJECTION METHOD Approximates Equidistant Conic, although it is commonly referred to as a Modified Transverse Mercator. LINES OF CONTACT The standard parallels at 53°30' N and 66°05'24" N. LINEAR GRATICULES The meridians are straight lines radiating from a center point. The parallels closely approximate concentric circular arcs. PROPERTIES Shape Neither conformal nor equal area. Area Neither conformal nor equal area. Direction Distortion increases with distance from the standard parallels. Distance Accurate along the standard parallels. 36 • Understanding Map Projections
ALBERS EQUAL A REA CONIC parallels are preserved, but because the scale along the lines of longitude does not match the scale along the lines of latitude, the final projection is not conformal. Area All areas are proportional to the same areas on the earth. Direction Locally true along the standard parallels. The central meridian is 96° W. The first and second standard parallels are 20° N and 60° N, while the latitude of origin is 40° N. DESCRIPTION This conic projection uses two standard parallels to reduce some of the distortion of a projection with one standard parallel. Although neither shape nor linear scale is truly correct, the distortion of these properties is minimized in the region between the standard parallels. This projection is best suited for land masses extending in an east-to-west orientation rather than those lying north to south. PROJECTION METHOD Conic. The meridians are equally spaced straight lines converging to a common point. Poles are represented as arcs rather than as single points. Parallels are unequally spaced concentric circles whose spacing decreases toward the poles. LINES OF CONTACT Two lines, the standard parallels, defined by degrees latitude. LINEAR GRATICULES All meridians. PROPERTIES Shape Shape along the standard parallels is accurate and minimally distorted in the region between the standard parallels and those regions just beyond. The 90 degree angles between meridians and Distance Distances are most accurate in the middle latitudes. Along parallels, scale is reduced between the standard parallels and increased beyond them. Along meridians, scale follows an opposite pattern. LIMITATIONS Best results for regions predominantly east–west in orientation and located in the middle latitudes. Total range in latitude from north to south should not exceed 30–35 degrees. No limitations on the east–west range. USES AND APPLICATIONS Used for small regions or countries but not for continents. Used for the conterminous United States, normally using 29°30' and 45°30' as the two standard parallels. For this projection, the maximum scale distortion for the 48 states is 1.25 percent. One method to calculate the standard parallels is by determining the range in latitude in degrees north to south and dividing this range by six. The ‘One-Sixth Rule’ places the first standard parallel at one-sixth the range above the southern boundary and the second standard parallel minus one-sixth the range below the northern limit. There are other possible approaches. Supported map projections• 37
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 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 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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Understanding Map Projections

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