Significance of Map Projections
Map projections are used to represent the surface of the earth. They are required for creating different types of maps. Because a dissected sphere cannot be evenly spread on a flat surface, all map projections distort the surface of the earth to some degree. Some distortions work for certain maps depending on the location the map is trying to portray. Map projections are used to most accurately portray the different properties of the planet earth. There are many types of map projections, the following are some examples: “Conformal” projections conserve angles and direction; “Equal-area” conserve area; and, “Equidistant” preserve distance but, distorts shape.
Mercator and Stereographic maps are examples of “Conformal” projections. They preserve the shapes of small objects but distort the shape and size of larger objects. These maps are useful when a person wants to know where the countries or continents are in relation to eachother. It would not be smart however, to rely on these maps to determine the and size of a country or region. The Stereographic version makes the northern and southern most regions of the globe appear to be much bigger than they truly are. The distance from Washington D.C. to Bagdad, Iraq in the Mercator projection is: 8,420.751647 miles, and 5,949.659306 miles in Sterographic.
To represent “Equal-area” projections, I used Cylindrical and Bonne maps. They are useful when trying to determine the area of a landmass. Sinusoidal maps can be used for both "Equal-area" and "Equidistant" projections. Bonne maps have a heart-like shape. They are not very common but, they do the job. The distance from Washington D.C. to Bagdad, Iraq in the Sinusoidal map is: 6,679.755121 miles, and 6,067.505247 miles in the Bonne map. They are not exactly the same but, very close.
Finally, I used a Carrée and, again, a Sinusoidal map as examples of “Equidistant” projections. The Carree map, according to Wikipedia, “preserves distance from some standard point.” The Sinusoidal map almost has the shape of a diamond being the widest at the equator. In this map the equator is not distorted. The distance from Washington D.C. to Bagdad, Iraq in the Carree map is: 8,411.550068 miles, and 6,679.755121 miles in the Sinusoidal map.
As I mentioned, every map projection is distorted one way or another. Conformal projections work best when the aim is to show direction; “Equal-area” when trying to show area; and “Equidistant” when trying to preserve distance between two points in the map. In order to be as accurate as possible, it is very important to know what projection would work best with the information we are trying to depict.
Coordinate Systems & Projections Worksheet
1. An ellipsoid is "a sphere that was slightly flattened at the poles." It is widest at the poles and flat on the north and south.
2. A Geographic Coordinate Systme.
3. "The magnetic north is the point towards which a compass points. The geographic North Pole is located at one of the poles of the Earth's axis of rotation."
4. "A datum is a 3-dimentional frame of reference used to determine surface locations. It attempts to approximate the ellipsoid."
5. A map projection is used to transffer locations from the curved earth's surface onto a flat surface.
6. A developable surface is one that "can be obtained from a plane sheet by deformation, without stretching or shrinking."
7. The lines of langitude.
8. GRS80 is the best model of the earth for the North American region.
9. The State Plane Coordinate Systme is more appropriate to use for developing and analyzing spatial data when mapping counties or larger areas; It is dessigned for specific regions of the U.S. and, "each state contains state plane zones, boundaries of which usually follow county lines."
10. A "great circle distance" is the shortest distance between two points on the surface of the globe.
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