Lab 5 - Projections

            Being a three-dimensional object, the earth cannot be readily represented on a two-dimensional surface like a map. In order to accomplish this task cartographers have developed projections using complex mathematical formulas. If you look at the maps above, you will note that each projection displays a different distance for the route between Washington DC and Kabul. This is because of differences in the mathematical calculations and the specific intentions of the cartographer. When working with a map projection you have to decide which real world features are most important. Is distance between two designated points most important or do you want that feature more generalized across the entire map? Cartographers have to take this and similar questions into account when they make their maps.

            Conformal projections, like the Mercator and Hotine projections above, attempt to preserve shape locally. These maps are popular but have limited use in doing good spatial analysis. The Mercator projection for example expands area as one moves away from the equator. The Hotine projection also displays similar area distortions.

            Equidistant projections, like the World Azimuthal Equidistant and World Equidistant Conic projections, have distance calibrated from the center of the map. From this calibrated center accurate distance is preserved. In the maps above however, neither Washington DC nor Kabul are at the center so accurate distance remains distorted.

            Equal area projections, like the Hammer Aitoff and Sinusoidal projections, aim to maintain consistent area. Compared to the Mercator or Hotine projection these maps represent the amount of area that each continent takes up on the globe more accurately. In terms of accuracy for distance these kinds of maps are also skewed.