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
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Mapping and Projections Web resources: Geographer’s Craft, Department of Geography, University of Colorado at Boulder - particularly Peter H. Dana’s part.
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Mapping and ProjectionsWeb resources:
Geographer’s Craft, Department of Geography, University of Colorado at Boulder - particularly Peter H.
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
Map Projections
•Basic problem:–Earth is round–Paper is flat
Conformal
Equivalent or Equal Area
Equidistant
Equidistant CylindricalMap from Carlo Futuri
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
Unprojected map
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
Cylindrical Projection
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.
Cylindrical Projection
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
Pseudocylindrical Projection
Pseudocylindrical Projection
Pseudocylindrical Projection
Conic Projection
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
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.
Conic Projection
Equidistant Conic Projection
Albers Equal Area Conic
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
Polyconic Projection
Polyconic Projection(centered at equator, 90ºW)
Azimuthal (Planar) Projection
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
Azimuthal Projection
Azimuthal Projection
Oblique Azimuthal Projection
Orthographic sort of means viewed from
infinite distance
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
Tangent Projection
Secant Projection
Secant Projection
Robinson Projection
Goode’s Interrupted Homolosine Projection
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