Lab 5 - Map Projections

Week 6 - Lab 5: Map Projections

As the title above states, this week's lab was all about different map projections. We learned how to create different map projections in ArcMap. Unlike last week, where we were given very explicit step by step instructions, this week we were more or less left to stumble our way through the software. Because it has been two weeks since our last lab, I had forgotten some of the things we had learned in ArcMap and had to spend some time re-learning general layout, controls, and functions.

The Earth, as we all know, is 3-D and spherical. Thus, it is impossible to create a two-dimensional representation of the Earth without some sort of distortion. Different projections distort different aspects of the map, and each projection is best for mapping certain things. Thus, depending on the situation, the "best" projection is usually a different one. It is for exactly this reason that ArcMap supports over 60 map projections.

There are three main categories or types of map projections: conformal, equal area, and equidistant. Conformal projections preserve angles. Equidistant projections maintain equal distances. Equal area projections maintain correct relative areas.

I will focus first on conformal projections. Conformal projections are characterized by the right angles at every intersection of a parallel and meridian. In order to preserve angles on the map, area and or distance are altered. For example, in the Mercator projection below, we see that Greenland appears much larger than it actually is. The distortion is very large near the poles. In the stereographic map neither distance nor area is preserved  Africa appears very small.  Conformal maps can be used in egocentric or propaganda maps to show certain areas as big and powerful or small and weak. They are also excellent for use in navigation.

Next we come to Equal Area projections. The two I have chosen to highlight below are the Cylindrical and Sinusoidal equal area projections.  In order to preserve area, distance and angles are compromised. These projections are useful when the size of a country or continent is important. In the cylindrical equal area projection, the area along the equator is not distorted, but other areas appear compressed.  In the sinusoidal projection, distortion is minimal along the prime meridian and equator.

Lastly, we come to the equidistant projections. In both the cylindrical and conic equidistant projections shown, distances from some relative point or line  on the map remain accurate in these projections. These maps can be confusing if the user is not clear on where the reference location is. These maps can easily be used incorrectly. The equidistant cylindrical projection preserves distances along the meridians, but no where else. The equidistant conic is convenient when mapping small countries, or for countries that extend mostly east-west, such as the former Soviet Union.