Analysis

About how many decimal degrees does the equator span?
- 360.01069 Decimal Degrees
What about the northern- or southern-most graticule line on the map?
- 180.49823 Decimal Degrees
Approximately how many miles separate Washington, D.C. and Afghanistan when crossing the Atlantic?
- 479.841   2420.881 Miles

There are all kinds of map projections, as seen in this lab. We know that a map projection represents the three dimensional curved surface of the Earth into a two dimensional flat surface. Each kind of map projection distorts at least one aspect of the real world: shape, area, distance, or direction. It depends on the map’s scale and purposes.

An equidistant projection maintains accurate distances from the center of the projection or along given lines. I illustrated the Equidistant Conic projection and the Plate Carree projection. The Plate Carree is centered at the Equator. The meridians are equally spaced vertical straight lines and the circles of latitude are evenly spread horizontal straight lines. One should not confuse it with equal area. The miles on the Plate Carree map and the GCS WGS 1984 are very similar. As you can see, the Equidistant Conic is a view of the Earth when looking straight down at the North Pole. A conic projection projects information from the spherical Earth to a cone that is either tangent to the Earth at a single parallel or that is secant at two standard parallels. It is then unwrapped to create the flat surface.

An Equal Area projection preserves the area. The same proportional relationship is maintained on the Earth and the map. From the center of the point, true directions are given. These maps are used when showing area accuracy is very important. I used the Bonne and Sinusoidal projections. The Bonne map is a pseudoconical equal area map. Its parallels of latitude are concentric circular arcs and the scale is true along these arcs. The central meridian and the standard latitude shapes are not distorted. The mileage is very different in the Sinusoidal and Bonne, with Sinusoidal showing 2692.676 miles and the Bonne only 608.51 miles. Clearly there is large distortion here.

A conformal projection preserves angles locally. It maintains angular relationships. Shapes over small areas are maintained but not in most areas. Parallels and meridians intersect at right angles and there is little distortion at the equator, although large distortions on the poles. In both the Mercator and Gall-Stereographic projections that I displayed, Greenland is much larger than Brazil (especially on the Mercator map).