Map Projections • Problem: Project a sphere onto a flat surface. • Scale • Alternative projection methods • Distortions • Terminology of map projections Maps - Resource A
Jan 03, 2016
Map Projections
• Problem: Project a sphere onto a flat surface.
• Scale
• Alternative projection methods
• Distortions
• Terminology of map projections
Maps - Resource A
Properties of the Globe Grid
• All meridians are of equal length; each is one-half the length of the equator.
• All meridians converge at the poles and are true north-south lines.
• All lines of latitude (parallels) are parallel to the equator and to each other.
• Parallels decrease in length as one nears the poles.
• Meridians and parallels intersect at right angles.
• The scale on the surface of the globe is the same in every direction.
Map Projections - Resource A
Geometrical (Perspective) Projections
• Graticule transferred to geometric shape and then the shape is cut and flattened.
• Developable surfaces
Map Projections - Resource A
Projection Classes
• Cylindrical
• Conic
• Planar (Azimuthal)
• Oval or Elliptical
Map Projections - Resource A
Map Projections - Resource A
Orthographic
• light source at infinity
Gnomonic
• light source at center
Stereographic
• light source at antipode.
Map Projections - Resource A
Mathematical Projections
• Emphasize and preserve elements of globe grid that perspective projections cannot.
Map Distortions of the Globe Grid Properties
• Equal Area (equivalent) - Preserves proportionate size but distorts shape.
• Shape (conformal) - Preserves true shape and directionality for small areas.
• Only maps for small areas can preserve both conformality and equivalence.
Map Distortions of the Globe Grid Properties (cont.)
• Distance (equidistant) - Correctly represent true great arc distances for one or two points on map. Distances between other points are distorted.
• Direction (azimuthal) - Preserve directionality radiating from one central point.
Gnomonic projection centered on Washington, DC. Great circle arcs are straight lines.
Map Projections - Resource A
Gnomonic
Examples Equal area sinusoidal
Azimuthal equidistant
Mercator (conformal)
Map Projections - Resource A
Examples Miller (cylindrical)
Albers equal area (conic)
Azimuthal Equidistant (planar)
Robinson Projection (oval)
Map Projections - Resource A