Tuesday, November 9, 2010

Geography 7 Assignment 5



The equator spans 360.05 degrees.
The prime meridian spans 180.52 degrees.
The equator represents the biggest latitude line, and the prime meridian is the biggest longitudinal line.
The measured distance of Washington D.C. to Kabul on the Spherical GCS Model was 6,935.96 miles.

Map projections are used to transform the 3D world into a 2D map. There are many ways to perform this task because the extensive amounts of mathematical conversions and shapes allow you to create a map that can preserve a certain quality. The three categories of projections we usually encounter are conformal, equal area, and equidistant map projections. A conformal map preserves the shapes and angles, while an equal area map will preserve the proportionality between the areas of the world. Lastly, an equidistant map projection will maintain the distance of places with respect to the center of the map. These projections can also vary in their developable surfaces since there are different types such as the plane, the cone, and the cylinder. With all this variation, there is no wonder why discrepancies arise.

In any case, map projections still have their advantages, and for a conformal map, the preservation of the angles and shapes come in handy when we fly or sail. The conformal map projections I used were the Mercator and Miller Cylindrical projections. The distance of Washington D.C. to Kabul on the Mercator projections was 10,117.62 miles. In the Miller Cylindrical projection, I measured the distance, the map read 10,225.50 miles. Although the map preserves angles and shapes, there is still a difference in the distance, which goes to show us that even within the same projection family the developable surface can distort a map.

For the equal area maps, I used the Cylindrical Equal Area and Bonne projections. Even though the areas are preserved in these two maps, the distances still varied. The Cylindrical Equal Area projection measured a distance of 10,114.45 miles from Washington D.C. to Kabul, which was closer to the Mercator projection than the Bonne projection which measured 6,739.75 miles. The equidistant maps had a similar map projection when it came to comparing the distances of Washington D.C. to Kabul. The Equidistant Conic projection was measured to be 6,986.08 miles, while the Equidistant Cylinder at 5,057.55 miles. Even as close as these projections were, there was still an inconsistency.

As we began to dive deeper into ArcGIS and the process of map making, the frustration levels start to rise, especially when we refer to the projections. Each projection is great in the sense that it can preserve a certain quality of the world when it is being transformed to the 2D surface. However, we tend to lose out no matter what the projection is. This goes to show how difficult it is to transform our 3D world to a simple 2D map. What that being said, how do we know which map projection is the best? There is no “best” projection, rather each particular projections gives the user the ability to extract the right information. For example, pilots and sailors would use the Mercator projection because that is the best representation of Earth that allows them to understand where they are during travel. With that being said, we should always be mindful of the maps we use because each map is different and unique and is distorted for a particular purpose. In some ways, this frustrates me because there are so many projections that I don’t have a clue what they are so I can’t use them. On the other hand, it is nice to see the world in the different perspectives. I just hope that one day map projections will combine and become one single representation of the world so that it can ease my mind when reading it.

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