Lab: Projection

     Since the earth is a spherical, it is hard to correctly represent it on the 2 dimension map. There is no way to perfectly project three-dimensional earth surface into a two-dimensional planer surface. However, two-dimensional maps are very important in geographical application. So we invented lots of map projection purposes. Each of projection methods has its specific purpose and serves different function. For more effective use of map, one must pick the right projection. In this lab, I used three types of projection to project a world map; they are equal-area projection, equal distance projection and conformal projection. By comparing the differences and similarities of these three maps, I will discuss the significance of map projection.

     The first projection is equal area projection. It accurately represents area in all regions of the sphere, but it does not accurately represent angles. It accurately represents area in all regions of the sphere, but it does not accurately represent angle and size of a region. Each equal area map preserves area in a certain region or with certain conditions. Therefore it is essential to choose the right equal area projection depending on your region of focus. In addition, different equal area projection maps have different appearances. For example, Sinusoidal projection is like an ellipse. The polar areas in this projection shrink a lot. The shapes of two polar areas are distorted. In Bonne equal area map, the world is projected as a heart-shape. The north polar is distorted even more. But in both of them, the areas are accurately preserved.

     The next is equal distance projection. A useful application for this type of projection is a polar projection in which all distances measured from the center of the map along any longitudinal line are accurate; as shown above,  a polar azimuthal equidistant projection and conic projection are good examples . These two projections project the world from the north polar. In these two maps, distances and directions to all places are true only from the center point of projection. Equidistant maps both shared a common trait: their degrees of measurement from Kabul, Afghanistan to Washington, D.C. are about the same in both of the maps. Distances are correct between points along straight lines through the center. Though they are not very useful for navigation because the shapes are not well preserved, they are very useful in polar projection.

   The last projection is conformal projection. It preserves the angle and shape. Conformal map projections are frequently employed in large-scale applications, and seldom used for continental or world maps. Because the shape does not change, it is pretty useful in navigation. It is a big advantage of this projection. But it also has disadvantage; the distance and size are largely distorted. For example, 1984 PDC Mercator projection, the distance from Kabul to Washington D.C. is much longer than the distance in other maps. Furthermore,  the south polar area is much bigger than usual. In the miller cylinder projection, it is the same; the south polar is distorted and the distance is relatively larger.