Week 5 Lab Assignment - Map Projections

When examining these six different map projections, it is easy to see how each map projection has certain advantages and disadvantages. Since a map projection is a 2D representation, it cannot perfectly represent our 3D Earth. Only certain properties of the data from the original GCS WGS 1984 shapefile will be preserved in the projection. These properties are affected by factors including the shape of the projection (planar, conic, etc) and the perspective. Each projection is more or less useful depending on what one is trying to learn from a map.

Conformal map projections preserve angle (or shape), meaning that the shape of land features is accurate while the area of features and the distance between certain points are not preserved. This is particularly obvious with the Mercator projection. The graticules are increasingly stretched vertically (in comparison to a 30º x 30º graticule) as one heads north of the Tropic of Cancer and south of the Tropic of Capricorn. Accordingly, land features further toward the top and bottom of the projection (Antarctica, Greenland, etc) are disproportionately large. In the Stereographic projection there is both horizontal and vertical distortion around the peripheries of the projection (it is most accurate around the intersection of the Equator and Prime Meridian, where its perspective is focused). This also affects distance as well. The real distance between Washington DC and Kabul is 6935 miles, but it is 8016 miles using the Mercator projection and 9878 miles using the Stereographic projection (both of which are conformal).

In equal area projections, like the Bonne projection, the graticules are all quite distorted (especially as one goes further from the intersection of the Prime Meridian and Equator) and the shape of the land features and the distance between them is not accurate. The advantages and disadvantages of this can easily be seen when one looks at New Zealand. Though the size of the country is accurate, its shape is obviously inaccurate. The distance between Washington DC and Kabul, though is more accurate in the Bonne projection than the Goodes Homolosine (Land) projection. Despite being the most inaccurate of these six projections in terms of the distance between DC and Kabul, Goodes Homolosine is one of my favorite projections. The shape of land forms is also quite well preserved and the graticules are closer to being 30º x 30º than they are in many of the other projections. I also like how it's design reminds viewers that they are looking at a 2D projection of a 3D object.

Finally, there are equal distance projections. As discussed in class with the example of the map showing North Korea's missile range, these maps can be very useful when distance is an important component of one's spatial analysis. For example, the Two-Point Equidistance map gives quite an accurate distance measurement between Washington DC and Kabul. However, the accuracy of distance measurements always varies depending on which particular distance measurements are preserved (there is no way to preserve all possible distance measurements on a 2D map projection using straight lines to measure distance). Area is also quite distorted with these maps, particularly with the Tangential Equal Distance map, where Australia appears to be larger than Antarctica. The graticules are very stretched vertically on this map, especially as one goes further east or west of the Prime Meridian.