Lab 5

The significance of map projections is that the projections transform three dimensional Earth into two dimensional maps. People can represent geographic information on a planar map and do spatial analysis using the maps. Therefore, map projections facilitate people’s activities by providing people with a two dimensional reference of their environment.

However, because projection is a process of mathematical conversion, there are inevitable distortions in every map projection.  For example, I made six world maps with different map projections and measured the distance between Washington, D.C. and Kabul on each map. I got six different results. For instance, the distance is 10,099.785 miles on Mercator but is 10,109.671 miles on Plate Carrée. The difference between these two projections is relatively small, as the distance is 6,730.704 miles on Bonne, which is much shorter than that on Mercator and Plate Carrée. From the distance between Washington, D.C. and Kabul, we can see how different projections are on maps. Therefore, people need to be careful when they use maps for information, especially when they need very accurate information.

Another disadvantage of projections is that people need to choose one that most suitable from many projections. Each projection has its own advantages and disadvantages. For Mercator and Plate Carrée, they are conformal map projections, so they preserve local shapes and angles. Yet conformal map projections do not preserve areas and distances between either two points. Bonne and Caster Parabolic are projections that preserve areas. In other words, areas on these maps maintain the same proportional relationship to areas on the Earth that they represent. However, those equal area projections do not preserve distances or shapes. Two-point Equidistant and Azimuthal Equidistant projections preserve the distances from the center of the projection to any place on the map, but the areas and shapes are distorted. Therefore, when select a specific projection, people need to figure out which attribution they need to be accurate. No projection can satisfy all the requirements. For example, if people require a map to preserve the areas, they should pick Bonne or other equal area projections instead of Mercator.

Although each projection has its own disadvantage, there is huge potential of projections. Because projections are based on different datum, it is important to make datum more accurate. As the geographic technology is developing, datum will become more and more accurate, and thus projections can apply to real world more accurately.