For Lab 5 we compared three different types of map projections and within each type we compared two different map projections. We used conformal, equal area, and equidistant projections. Conformal projections preserve the angles describing the spatial relationship, equal area projections preserve the area of the displayed feature, and equidistant projections preserve the distance between certain points on a map. In order to preserve these specific attributes, other properties are distorted, such as scale, shape, or angle. Each map projection has its own advantages and disadvantages, and certain projections are more accurate than others depending on where in the world and what type of data is being analyzed.
In the first set of projections, right angles in the graticule lines are preserved. Although the local shapes are accurate in the stereographic projection, it is most accurate at the center, with increasing distortion with distance. For better accuracy, it should also generally be limited to one hemisphere. The Mercator projection, one of the most commonly seen projections, is useful because it represents the world as a flat rectangle, which is nice for illustrative purposes; however, in doing so it is highly distorted. The area is especially affected, for example, it depicts the United States as nearly the size of Africa; however, the United States is actually much smaller than Africa.
The second set, the equal area projections, preserve the area of the features, but distorts the shape, among other properties. Looking at the Eckert IV projection can give a better representation of the sizes of the United States and Africa, compared to the Mercator projection. The Eckert projection stretches the shape towards the equator, while compressing it vertically towards the poles. Although it preserves area, it distorts mostly everything else, making it mostly useful as a world map, like the Mercator projection. In the Sinusoidal projection, there is no distortion along the equator and central meridian, but there is elsewhere. The shapes are heavily distorted towards the edges, especially the western Americas and eastern Europe and Asia. Like most projections, it is best to use on a single area rather than the whole world.
In the Equidistant Conic projection, distance is true along standard parallels and the meridians. It is most accurate east to west among midlatitude areas. For this reason, it is a good choice for mapping the distance between Washington, D.C. and Kabul, Afghanistan, and measured it at 6,972.48 miles, while the actual distance is 6,956.6 miles; just over 20 miles off. Similarly, the Two Point equidistant projection is much closer than either of the equal area or conformal projections. This lab demonstrates the importance of choosing the best projection for the type of analysis one is doing, as different projections preserve certain properties, but to do so distort others. The conformal projections distorted nearly all properties, and were both over 3,000 miles off, while the equidistant were very close, and the equal area were between both.
