Lab 5: Map Projections

Map projections are a necessary part of creating maps and very useful in ArcGIS. They are useful because they let someone visualize a three-dimensional globe on a 2-d plane. However, although map projections are useful, there are also pitfalls to transferring a 3-d object onto a 2-d plane. No matter how you project the globe onto a plane, distortions in your map are bound to happen.

A map can be projected in many ways and each is suitable for different situations. Conformal maps such as the WGS 1984 Mercator and Mercator projections illustrated above preserve the angles of points at small distances. Pilots can find these maps useful because the angle at which they turn is very important. However, pilots favor maps, such as the Lambert Conformal conic projection, that are both conformal and equidistant. Equidistant maps, such as the equidistant conic and cylindrical projections, preserve the distance of places to each other. A pilot would find an equidistant conformal map projection useful because it would increase accuracy in the angle they have to turn and the distance they have to travel. In addition, there are also maps that preserve area, such as the sinusoidal and Mollweide projections above.

Projections can also be categorized into the type of surface used to project them. Sinusoidal projections keep the north-south and east-west scales the same. Cylidrical projections tend to stretch distances east to west when meridians are mapped to equally spaced vertical lines. An interesting trait about these was that the length of each longitude line was the same no matter how far from the equator. This did not happen with the Sinusodial projection. Conical projections can help minimize distortion from projecting a 3-dimensional object to a 2-dimensional surface.

Map projections must be made to suit the user's needs. As mentioned earlier, pilots may prefer the Lambert conformal conic projection, while the Mollweide projection provides a neater view for world maps. Overall, the main thing to look at is what part of the globe you need preserved. Whether it is area, distance, angles, or even a mixture of them all. Once you have established your need, you can choose the projection most suitable for you.