Lab 5

Measurements of the distance between Washington, D.C. and Kabul

A map projection is a process that transforms the 3-D irregular sphere, Earth, into a 2-D flat surface, which is easier to work on than a 3-D model of Earth. Map projections are very important for us to understand features on Earth based on a 2-D ground, such as the relative positions of two continents and the distance between two chosen coordinates. A projection can be classified by the type of projection surface, onto which the globe is conceptually projected. Some of the surfaces that are frequently used are planes, cones and cylinders. The three sets of maps shown above are classified as conformal, equal-area and equidistant according to the properties of the model they preserve. Each of the three kinds has its own certain advantage of learning a particular feature on the map.

The conformal map projections, for example, preserve angles locally. As we can see on both the Mercator and stereographic maps, the pairs of meridian lines and parallel lines are always intersecting at 90 degrees. Thus, conformal maps are usually quite useful to guide our directions and find relative positions of two coordinates, especially over small areas. The equal-area map projections preserve area on maps. Like the Behrmann equal area cylindrical map and the cylindrical equal area map, area is maintained. Therefore, we can compare the real areas of two regions on those maps in a relatively accurate way. Equidistant projections preserve distance from some standard points or lines.  While the equidistant conic projection can be based on one or two standard parallels, the two-point equidistant projection shows the true distance from either of two chosen points to any other point on a map. The planar distance between Washington, D.C. and Kabul on the equidistant conic map is 6972.48 miles, which is closest to the true distance between the two places among all the six projections.

As we already know, all the map projections have some certain degree of distortion. Take the Mercator projection for example. Although the projection maintains local angular relationship, area on this map is distorted. How could Greenland be larger than China or Australia?  For the equal area projections, there is always some distortion of shape and direction on maps. For example, the cylindrical equal area map has severe distortion of shape and scale near the poles and the distances are generally distorted except along the equator on the Behermann equal area cylindrical projection. Both of the equidistant projections contain some sort of distortion on shape and area. We can see that all those kinds of distortion could lead to people’s misunderstanding of the true geographical properties of the world. This is a potential peril we should certainly avoid. Thus, it is truly crucial to select a projection to meet our purposes or interests of an analysis.

Despite the unavoidable flaws of any of the map projections, map projections offer us great insight into geographical properties of our world. By using different sorts of projections, we can focus on analyzing different spatial information to meet our target goals. Thus, map projections have the potential to allow us to compare distinct features of Earth and broaden our knowledge on our positions and surrounding areas.