Lab HW5

The real distance between two cities is 11195600m
 Conformal Projection Map:

Distance:16256949m

Distance: 16347217m

 Equal Area Projection Map:

Distance:12733317m

  

Distance:16277532m

 Equidistant Projection Map:

Distance:10821337m

 

Equatorial Azimuthal Equidistant Projection Distance: 13382251m

    This week's homework is make 6 different projection maps, it seems an easy work because we just follow the same procedure and just switch between different projections that are already stored in ArcGIS.

    However, I really find the importance of the choice of projection from it. Basically, the most obvious different between them is three different types: conformal, equidistant and equal area. I can conclude easily from the measure tool in ArcGIS to tell that with different projection distant between two points may vary significantly. As six projections I chose, the distance between them varies from 10821337m to 16347217m. However, the real distance turns out to be 11195600m and none of six projections above gives the true value(it may be also due to the error in my measure). So that it's hard to have same distance using different projections even they are divided into similar category.

    Besides, it really challenged my impression of map. Because I always using city or road map to find direction, I took for granted that maps look similar and every information in it is accurate. So I was truly surprised when I saw those lovely and rare, for me, projections such as two points equidistant. It's much better to know from lab than ppt in lecture because I can change myself, choose whatever I want and see their information. 

    Moreover, I find within same category, there's still very big difference. their functions are also significantly different. For example, Two Point Equidistant Projection Map and Equatorial Azimuthal Equidistant Projection Map are both equidistant map, but they have very different function. The former is  commonly used in National Geographic Society atlases for maps of Asia, and it sometimes appears in diagrams of air routes, the later is useful for showing airline distances from center point of projection and for seismic and radio work.

    Finally, I can see from those different projection maps that how significant projection is. Different choice of projection can result in totally different map with various functions. And I realize it's still a tricky problem in projection since no single projection can preserve all three types of data. Maybe 3D map can help, but it's still a long way to go because it require a very strong infrastructure, for now, to make it prevalent.