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Map Projections

An overview of different map projections; how they are produced and applications of each.

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Map Projections

  1. 1. Map Projections<br />
  2. 2. Projections<br /><ul><li>Projecting is the science of converting the spherical earth surface to a flat plane</li></li></ul><li>Projections<br />No system can do this perfectly. Some distortion will always exist.<br />Properties that are distorted are angles, areas, directions, shapes and distances.<br />Each projection distorts one or more of these while maintaining others.<br />Selecting a projection is based on selecting which needs to be preserved.<br />
  3. 3. Developable Surfaces<br />A surface that can be made flat by cutting it along certain lines and unfolding or unrolling it.<br />Cones, Cylinders, & Planes are all developable surfaces.<br />
  4. 4. Developable Surfaces<br />Projection families are based on the developable surface that is used to create them<br /><ul><li>Cones = conical projections
  5. 5. Cylinders = cylindrical projections
  6. 6. Planes = azimuthal or planar projections</li></li></ul><li>Projection Families<br />
  7. 7. Idea of Light Source<br />Gnomonic:The projection center is at the center of the ellipsoid.<br />Stereographic: The projection center is at the opposite side<br />opposite the tangent point.<br />Orthographic:The projection center is at infinity.<br />
  8. 8. Types of Projections<br />Distortion is unavoidable<br /><ul><li>Conformal—where angles are preserved
  9. 9. Equal Area (equivalent)—where areas are preserved.
  10. 10. Equidistance—where distance is preserved between two points.</li></li></ul><li>The Variables in Map Projection<br />Gnomonic<br />Plane<br />Light Source<br />Projection Surface<br />Stereographic<br />Cylinder<br />Varieties ofgeometric projections<br />Orthographic<br />Cone<br />Transverse ObliqueNormal<br />Projection Orientation or Aspect<br />
  11. 11. Map Projection Distorts Reality<br />A sphere is not a developable solid.<br />Transfer from 3D globe to 2D map must result in loss of one or global characteristics:<br />Shape<br />Area<br />Distance<br />Direction<br />Position<br />
  12. 12. Tissot'sIndicatrix<br />Circles plotted on a globe will remain circular.<br />Circles plotted on a map will be distorted, either by area, shape or angle. <br />
  13. 13. Characteristics of a Globe to consider as you evaluate projections<br />Scale is everywhere the same:<br />all great circles are the same length<br />the poles are points.<br />Meridians are spaced evenly along parallels.<br />Meridians and parallels cross at right angles.<br />
  14. 14. Characteristics of globe to consider as you evaluate projections<br />a<br />b<br />Quadrilaterals equal in longitudinal extent formed between two parallels have equal area.<br />Area of a = area of b<br />
  15. 15. Pole<br />e<br />d<br />c<br />b<br />a<br />0°<br />20°<br />Characteristics of globe to consider as you evaluate projections<br />Areas of quadrilaterals formed by any two meridians and sets of evenly spaced parallels decrease poleward.<br />Area of a > b > c > d >e<br />
  16. 16. Classification of Projections<br />Projections are classed by <br />the global characteristic preserved.<br />Geometric approach to construction.<br />projection surface<br />“light” source<br />Orientation.<br />Interface of projection surface to Earth. <br />
  17. 17. Global Characteristic Preserved<br />Conformal (Shape)<br />Equivalent (Area)<br />Equidistant (Distance)<br />Azimuthal (Direction)<br />
  18. 18. Conformal Projections<br />Retain correct angular relations in transfer from globe to map.<br />Angles correct for small areas.<br />Scale same in any direction around a point, but scale changes from point to point.<br />Parallels and meridians cross at right angles.<br />Large areas tend to look more like they do on the globe than is true for other projections.<br />Examples: Mercator and Lambert Conformal Conic<br />
  19. 19. Mercator Projection<br />
  20. 20. Lambert Conformal Conic Projection<br />
  21. 21. Equivalent or Equal Area Projections<br />A map areaof a given size, a circle three inches in diameter for instance, represents same amount of Earth space no matter where on the globe the map area is located. <br />Maintaining equal area requires:<br />Scale changes in one direction to be offset by scale changes in the other direction.<br />Right angle crossing of meridians and parallels often lost, resulting in shape distortion.<br />
  22. 22. Pole<br />Projection<br />e<br />Pole<br />d<br />c<br />b<br />a<br />0°<br />20°<br />0°<br />20°<br />Area of a > b > c > d >e<br />Maintaining Equal Area<br />Globe<br />Map<br />
  23. 23. Mollweide Equivalent Projection<br />
  24. 24. Equivalent & Conformal<br />Preserve true shapes and exaggerate areas<br />Show true size and squish/stretch shapes<br />OR<br />
  25. 25. Equidistant Projections<br />Length of a straight line between two points represents correct great circle distance.<br />Lines to measure distance can originate at only one or two points.<br />
  26. 26. Plane Surface<br />Earth grid and features projected from sphere to a plane surface.<br />
  27. 27. Plane Projection<br />Equidistant<br />Azimuthal<br />
  28. 28. Plane Projection: Lambert Azimuthal Equal Area<br />
  29. 29.
  30. 30. Azimuthal Projections<br />North<br />Straight line drawn between two points depicts correct:<br />Great circle route<br />Azimuth<br />Azimuth = angle between starting point of a line and north<br />Line can originate from only one point on map.<br /><br />Azimuth of green line<br />
  31. 31. Azimuthal Projection <br />Centered on Rowan<br />Great Circle<br />
  32. 32. Great CircleFlight Path<br />
  33. 33. Plane Projection: Lambert Azimuthal Equal Area<br />Globe<br />Projection to plane<br />
  34. 34. Conic Surface<br />Globe projected onto a cone, which is then flattened.<br />Cone usually fit over pole like a dunce cap.<br />Meridians are straight lines.<br />Angle between all meridians is identical.<br />
  35. 35. Conic Projections<br />Usually drawn secant.<br />Area between standard parallels is “projected” inward to cone.<br />Areas outside standard parallels projected outward.<br />
  36. 36.
  37. 37. Equidistant Conic Projection<br />
  38. 38. Cylinder Surface<br />Globe projected onto a cylinder, which is then flattened.<br />Cylinder usually fit around equator.<br />Meridians are evenly spaced straight lines.<br />Spacing of parallels varies depending on specific projection.<br />
  39. 39. Miller’s Cylindrical Projection<br />
  40. 40. “Light” Source Location<br />Gnomonic: light projected from center of globe to projection surface.<br />Stereographic: light projected from antipodeof point of tangency.<br />Orthographic: light projected from infinity.<br />
  41. 41. Gnomonic Projection<br />
  42. 42. Gnomic Projection<br />
  43. 43. Gnomic Projection<br />Mercator Projection<br />
  44. 44. Stereographic Projection<br />
  45. 45. Stereographic Projection<br />
  46. 46. Stereographic Projection<br />
  47. 47. Orthographic Projection<br />
  48. 48.
  49. 49.
  50. 50. Normal Orientation<br />
  51. 51. Mercator Projection<br />
  52. 52. Transverse Orientation<br />
  53. 53. Transverse Spherical Mercator<br />
  54. 54. Oblique Orientation<br />
  55. 55. Often used to map a specific area. Oblique orientations are used to map the linear swath captured by an earth observing satellite. <br />
  56. 56. The Variables in Map Projection<br />G<br />P<br />Projection Surface<br />Light Source<br />S<br />Cyl<br />Varieties ofgeometric projections<br />O<br />Cone<br />TO N<br />Projection Orientation or Aspect<br />
  57. 57. Projection Selection Guidelines<br />Determine which global feature is most important to preserve [e.g., shape, area].<br />Where is the place you are mapping:<br />Equatorial to tropics = consider cylindrical<br />Midlatitudes = consider conic<br />Polar regions = consider azimuthal<br />Consider use of secant case to provide two lines of zero distortion.<br />
  58. 58. Example Projections & Their Use<br />Cylindrical<br />Conic<br />Azimuthal<br />Nongeometric or mathematical<br />
  59. 59. Cylindrical Projections<br />
  60. 60. Cylindrical Projections<br />Equal area:<br />Cylindrical Equal Area<br />Peters [wet laundry map].<br />Conformal:<br />Mercator<br />Transverse Mercator<br />Compromise:<br />Miller<br />
  61. 61. Cylindrical Projections<br />Cylinder wrapped around globe:<br />Scale factor = 1 at equator [normal aspect]<br />Meridians are evenly spaced. As one moves poleward, equal longitudinal distance on the map represents less and less distance on the globe.<br />Parallel spacing varies depending on the projection. For instance different light sources result in different spacing.<br />
  62. 62. Peters ProjectionCylindrical – Equal Area<br />
  63. 63. Central Perspective Cylindrical<br />Light source at center of globe.<br />Spacing of parallels increases rapidly toward poles. Spacing of meridians stays same.<br />Increase in north-south scale toward poles.<br />Increase in east-west scale toward poles.<br />Dramatic area distortion toward poles.<br />
  64. 64. Mercator Projection<br />Cylindrical like mathematical projection:<br />Spacing of parallels increases toward poles, but more slowly than with central perspective projection.<br />North-south scale increases at the same rate as the east-west scale: scale is the same around any point.<br />Conformal: meridians and parallels cross at right angles. <br />Straight lines represent lines of constant compass direction: loxodrome or rhumb lines.<br />
  65. 65. Mercator Projection<br />
  66. 66. Gnomonic Projection<br />Geometric azimuthal projection with light source at center of globe.<br />Parallel spacing increases toward poles.<br />Light source makes depicting entire hemisphere impossible.<br />Important characteristic: straight lines on map represent great circles on the globe.<br />Used with Mercator for navigation :<br />Plot great circle route on Gnomonic.<br />Transfer line to Mercator to get plot of required compass directions.<br />
  67. 67. Gnomonic Projection with Great Circle Route<br />Mercator Projectionwith Great Circle RouteTransferred<br />
  68. 68. Cylindrical Equal Area<br />Light source: orthographic.<br />Parallel spacing decreases toward poles.<br />Decrease in N-S spacing of parallels is exactly offset by increase E-W scale of meridians. Result is equivalent projection.<br />Used for world maps.<br />
  69. 69.
  70. 70. Miller’s Cylindrical<br />Compromise projection near conformal<br />Similar to Mercator, but less distortion of area toward poles.<br />Used for world maps.<br />
  71. 71. Miller’s Cylindrical Projection<br />
  72. 72. Conic Projections<br />
  73. 73. Conics<br />Globe projected onto a cone, which is then opened and flattened.<br />Chief differences among conics result from:<br />Choice of standard parallel.<br />Variation in spacing of parallels.<br />Transverse or oblique aspect is possible, but rare.<br />All polar conics have straight meridians.<br />Angle between meridians is identical for a given standard parallel.<br />
  74. 74. Conic Projections<br />Equal area:<br />Albers<br />Lambert<br />Conformal:<br />Lambert<br />
  75. 75. Lambert Conformal Conic<br />Parallels are arcs of concentric circles.<br />Meridians are straight and converge on one point.<br />Parallel spacing is set so that N-S and E-W scale factors are equal around any point.<br />Parallels and meridians cross at right angles.<br />Usually done as secant interface.<br />Used for conformal mapping in mid-latitudes for maps of great east-west extent.<br />
  76. 76.
  77. 77. Lambert Conformal Conic<br />
  78. 78. Albers Equal Area Conic<br />Parallels are concentric arcs of circles.<br />Meridians are straight lines drawn from center of arcs.<br />Parallel spacing adjusted to offset scale changes that occur between meridians.<br />Usually drawn secant.<br />Between standard parallels E-W scale too small, so N-S scale increased to offset.<br />Outside standard parallels E-W scale too large, so N-S scale is decreased to compensate.<br />
  79. 79. Albers Equal Area Conic<br />Used for mapping regions of great east-west extent.<br />Projection is equal area and yet has very small scale and shape error when used for areas of small latitudinal extent.<br />
  80. 80.
  81. 81. Albers Equal Area Conic<br />
  82. 82. Albers Equal Area Conic<br />Lambert Conformal Conic<br />
  83. 83. Modified Conic Projections<br />Polyconic:<br />Place multiple cones over pole.<br />Every parallel is a standard parallel.<br />Parallels intersect central meridian at true spacing.<br />Compromise projection with small distortion near central meridian.<br />
  84. 84. 7<br />Polyconic <br />
  85. 85. Polyconic<br />
  86. 86. Azimuthal Projections<br />
  87. 87. Azimuthal Projections<br />Equal area:<br />Lambert<br />Conformal:<br />Sterographic<br />Equidistant:<br />Azimuthal Equidistant<br />Gnomonic:<br />Compromise, but all straight lines are great circles.<br />
  88. 88. Azimuthal Projections<br />Projection to the plane.<br />All aspects: normal, transverse, oblique.<br />Light source can be gnomonic, stereographic, or orthographic.<br />Common characteristics:<br />great circles passing through point of tangency are straight lines radiating from that point.<br />these lines all have correct compass direction. <br />points equally distant from center of the projection on the globe are equally distant from the center of the map.<br />
  89. 89. Azimuthal Equidistant <br />
  90. 90. Lambert Azimuthal Equal Area<br />
  91. 91. Other Projections <br />
  92. 92. Other Projections<br />Not strictly of a development family<br />Usually “compromise” projections.<br />Examples:<br />Van der Griten<br />Robinson<br />Mollweide<br />Sinusodial<br />Goode’s Homolosine<br />Briesmeister<br />Fuller<br />
  93. 93. Van der Griten<br />
  94. 94. Van der Griten<br />
  95. 95. Robinson Projection<br />
  96. 96. Mollweide Equivalent Projection<br />
  97. 97. Sinusoidal Equal Area Projection <br />
  98. 98.
  99. 99. Briemeister<br />
  100. 100. Fuller Projection<br />