LAB WEEK 6: Geospatial Data Management

What is the distance from Washington DC to Kabul? By looking at the above maps you would be lost with an answer that ranges from 5,060 miles to 10,153 miles. So what’s the real distance? It is 6,502 miles. The Bonne map projection came closest to this number. However, every map projection has its “issues”.

There are three main types of map projections: conformal, equal-area, and equidistant projections. The 90º angles (right angles) of the longitudinal and longitudinal lines are characteristic of conformal map projections. Conformal maps preserve angles, but not distance. For this reason, you can understand why the distance between the two cities is so incorrect on the projection. The Mercator projection, which is a conformal projection type, has the largest distance. You can also tell that the map itself is distorted because Antarctica is the size of almost the rest of the land mass on the earth, which is definitely not true in reality.

Equidistant map projections are characterized by a uniform distance from the center of the map to all other places on the map. The two equidistant map projections that I choose were Aitoff and Equidistant Cylindrical. As you can tell, they look very different, but both fit in within the guidelines of what qualifies as an equidistant projection. Equidistant projections preserve area from a standard point or line, which is usually the center. However, while this type of projection preserves distances on the map itself, these distances do not closely resemble reality, which is why the measurements between the two cities are so off.

The third type of map projection is known as equal area. An equal area projection attempts to maintain the same proportional relationships to the areas on the Earth that they represent. Because of this, the equal area projections are closest to reality. This explains why the Bonne projection comes closest to the correct Washington DC – Kabul distance. Of all the six map projections I would also have to vote for the Mollweide projection as looking the most realistic. Everything looks more or less laid out to the proper scale, unlike the – projection where Alaska looks like it is as big as Australia.

Overall, I enjoyed this lab. Once I got the hang of it (because I had to keep starting over for different reasons) I could fly through making the projections. I feel like a much better sense of ArcGIS since the last lab. I felt that I could actually maneuver through the program without needing to constantly be referring back to a tutorial. However, if there was a tutorial I would have probably heavily relied on it, which is why it is good that this lab didn’t include one. I felt that this way I learned more.