1. Maps - Resource A
Map Projections
Problem: Project a sphere onto a flat surface.
Scale
Alternative projection methods
Distortions
Terminology of map projections

3. Map Projections - 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.

4. Map Projections - Resource A
Geometrical (Perspective) Projections
Graticule transferred to geometric shape and then the shape is cut and flattened.
Developable surfaces

5. Map Projections - Resource A
Projection Classes
Cylindrical
Conic
Planar (Azimuthal)
Oval or Elliptical

6. Map Projections - Resource A
Orthographic
light source at infinity
Gnomonic
light source at center
Stereographic
light source at antipode.

7. 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.

8. Map Projections - Resource A
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
Gnomonic projection centered on Washington, DC. Great circle arcs are straight lines.

9. Map Projections - Resource A
Examples
Equal area sinusoidal
Azimuthal equidistant
Mercator (conformal)

10. Map Projections - Resource A
Examples
Azimuthal Equidistant (planar)
Miller (cylindrical)
Robinson Projection (oval)
Albers equal area (conic)