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Mapping and Projections

Mapping and Projections. Web resources: Geographer’s Craft, Department of Geography, University of Colorado at Boulder - particularly Peter H. Dana’s part http://www.colorado.edu/geography/gcraft/contents.html

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Mapping and Projections

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  1. Mapping and Projections Web resources: Geographer’s Craft, Department of Geography, University of Colorado at Boulder - particularly Peter H. Dana’s part http://www.colorado.edu/geography/gcraft/contents.html Laurie Garo, Map Projections module, in Virtual Geography Department, U. of Texas at Austin (hosted at U. of Colorado) http://www.colorado.edu/geography/virtdept/contents.html

  2. Map Projections • Basic problem: • Earth is round • Paper is flat

  3. Conformal

  4. Equivalent or Equal Area

  5. Equidistant

  6. Equidistant CylindricalMap from Carlo Futuri

  7. Solving the Problem • How do you represent a curved surface on a flat surface? • Bonehead way - just plot latitude vs. longitude as cartesian rectangular coordinates • Projection - fit a flat surface around (or through) a sphere, and trace the pertinent information on it

  8. Unprojected map

  9. Types of projections • Three main families: • Cylindrical - wrap sheet of paper around globe in cylinder shape • Also pseudocylindrical - like cylindrical but the sheet of paper bends inward at the poles • Conic - form sheet of paper into a cone and insert globe • Also polyconic - multiple cones • Azimuthal - place flat sheet of paper next to globe; project features out onto it

  10. Cylindrical Projection

  11. Cylindrical Projection • Formed by wrapping a large, flat plane around the globe to form a cylinder. • Transfer latitude, longitude, shapes onto cylinder, then unfolded into a flat plane. • Typically used to represent the entire world; often projected from center of globe with equator as tangent line • Most types show parallels and meridians forming straight perpendicular lines.

  12. Cylindrical Projection

  13. Pseudocylindrical Projection • Projection surface is not rectangular • Instead, it curves inwards at the poles. • Latitude lines are straight; central meridian is straight, but other meridians are curved (concave toward the central meridian). • Often used for world maps

  14. Pseudocylindrical Projection

  15. Pseudocylindrical Projection

  16. Pseudocylindrical Projection

  17. Conic Projection

  18. Conic Projection • Points from the globe are transferred to a cone fit around the sphere. • Usually, the pointy end of the cone is directly over the north or south pole, but you can do it anywhere. • Can represent both hemispheres, but distortion increases the farther along the cone you go

  19. Conic Projection • Often used to project areas that have a greater east-west extent than north-south, e.g., the United States. • When projected from the center of the globe, conic projections typically show parallels forming arcs concave toward the North or South pole, and meridians are either straight or curved and radiate outwards from the direction of the point of the cone.

  20. Conic Projection

  21. Equidistant Conic Projection

  22. Albers Equal Area Conic

  23. Polyconic Projection • Complex projection, used originally by USGS for quadrangle maps of U.S. • Uses an infinite number of cones applied to an infinite number of tangents across a given hemisphere • Reduces distortion, but harder to conceptualize and produce

  24. Polyconic Projection

  25. Polyconic Projection(centered at equator, 90ºW)

  26. Azimuthal (Planar) Projection

  27. Azimuthal or Planar Projection • Globe grid is projected onto a flat plane • Plane is normally placed above the north or south pole, so normally only one hemisphere, or a portion of it, is represented • When projected from the center of the globe, a typical polar azimuthal projection shows circular latitude lines with radiating longitude lines

  28. Azimuthal Projection

  29. Azimuthal Projection

  30. Oblique Azimuthal Projection Orthographic sort of means viewed from infinite distance

  31. Types of projections • Tangent • Flat surface only touches globe along one circular line (or at one point for Azimuthal) • Secant • Flat surface passes through globe; touches surface at two circular lines (or in one circle for Azimuthal) • Some projection is inward rather than outward • Reduces distortion of large areas

  32. Tangent Projection

  33. Secant Projection

  34. Secant Projection

  35. Robinson Projection

  36. Goode’s Interrupted Homolosine Projection

  37. Tissot indicators • Tissot’s idea - to see the effects of distortion, show what shape small circles on the surface of the globe take after projection • This shows shape, scale, area, and other distortions

  38. Tissot Indicators – Mercator (Conformal) Image from http://quantdec.com/tissot

  39. Tissot Indicators – Peters Equal Area Image from http://quantdec.com/tissot

  40. Tissot Indicators – Azimuthal Equidistant Image from http://quantdec.com/tissot

  41. Tissot Indicators

  42. Silly Projections

  43. Web sites to visit: • http://www.guilford.edu/geology/Geo340.html

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