Lab5:Projections In ArcGIS

  With no projection, the distance (D) between Washington, D.C. and Kabul is 6936.35 miles 

World Equal Distance Cylindrical Projection:(D)=5068.2miles
World  Equal Distance Conic Projection:(D)=7021.4miles

World Cylindrical Projection: (D)=10120.3 miles
Mollweide Equal Area Projection:(D)=7930.84miles 

WGS 1984 Web Mercator Projection: (D)=10119.7miles
Mercator Projection (D)=10119.6miles

          

            In Lab5, different projections of world map is created by using ArcGIS. Map projection is the methods and procedures that are used to transform the spherical three-dimensional earth into two-dimensional planar objects,  such as paper, and computer screen. However, there are no perfect method to project a three-dimensional object into two-dimensional without any distortion, so different map projections have different preservations. There are three main types of map projections. They are: Equal distance projection, preserving distance; Equal area projection, preserving area; and Conformal projection, preserving direction.

                Map projections are significantly important in map making, because different maps have different usages, and different preservations. Like in this lab, one of the purpose is measuring the distance between Washington, D.C. and Kabul in different map projection. The actual distance between the two cities is 6936miles. As the data above, the distance error of conformal projection and equal area projection is large. The delta D can up to about 3000miles. Also, not all equal distance projection can be used to measure the distance between  Washington, D.C. and Kabul, because there are two types of equal distance projections, longitude preserving and latitude. In this lab, the distance between Washington, D.C. and Kabul is along the latitude, so the World Equal Distance Cylindrical Projection is not doing a good measurement because it is a longitude preserving projection. But the measurement of World Equal Distance Conic projection is quite close to the actual value(actual=6936miles, measure=7021miles). From this, the significance for the map projection can be understood, and different kinds of map projections do make a different in measurements.

                In this lab, it is needed to do some research on projections of map. In ArcGIS, there are a lot of projections can be used in ArcGIS, and I found out that there are not only conformal, equal area, and equal distance projection, but also some other projection, for example, Gall's Stereographic Projection; this projection preserve in both shape(area), distance, and direction, but these preservations are only true at latitude 45N and S. In the other places other then latitude 45N and S, most of the distance, shape, and direction are generally distorted. Knowing which projection is the map used, and understanding how the projection work out is the only way to avoid the peril of using the wrong map projection.

            All in all, map projection is a fundamental topic in Geographical information system. I think there are still a lot of improvements can be done in map projection since until now, there is no perfect projection can use to represent the three-dimensional world. With the advance technology in the future, may be there are some two-dimensional object can turn into a globe and it can show the real world with no distortion.