Lab 5: Projections in ArcGIS

Write Up: Projections in ArcGIS

Write four paragraphs about the significance of map projections. Be sure to reference your six maps as examples.

     Each map projection has its own purpose. Some give accurate depictions of area or shape. Other projections give accurate distances between points.If used properly, map projections can elucidate geographic relationships. At the same time, a map projection used incorrectly will give misleading data that can greatly skew lab data.

     Perhaps the best example of map distortion is the Mercator distortion. Along the equator, the map is relatively accurate in its shapes and size of land masses. However, continents like North America that stretch from North to South are particularly distorted. This could lead to inaccurate assumptions, such as extrapolating that North America is larger than Africa. In reality, Africa is much larger by 2,243,000 square miles. (enchantedlearning.com) Rather than using only one projection, an individual must use several projections to answer geographic questions. 

     I encountered map distortion in the lab when I measured the distance between Washington DC, USA and Kabul, Afghanistan. According to Google Earth, the distance is close to 6956.6 miles. The Fuller projection underestimated this distance at 6363.79 miles. The Stereographic projection overestimated this distance at 9878.04 miles. The Azithumal, Flat Polar Quartic, and Sinusoidal projections estimated, on average, 8212.34 miles. The Equidistant Planar projection, as per its name, was closest to the accepted value with an estimate of 6972.48 miles. Clearly, the correct projection must be used in finding data. An equidistant projection should be used to find distances.

     If an individual uses the proper map projection for his data then he will avoid misleading calculations. Each map must be used for its specific purpose and nothing else. In the lab scenario, I should have used the equidistant map to determine the distance between DC and Kabul. The other maps were meant for different purposes and should have been ignored. 

Sources:

http://www.enchantedlearning.com/geography/continents/Land.shtml