Lab 5 : Projections in ArcGIS

Map projections are necessary for creating maps. A map projection involves the process of representing the surface of a shape (ie. sphere, cone, cylinder, etc.) onto a plane. However, in this process distortions are inevitable. Below are some examples of different map projections, showing how certain projections are more useful for certain activities.

The two above maps (Gall Stereographic and Mercator) are examples of conformal map projections. Conformal map projections preserve angles, but have the tendency to distort area and distance. The reason for this is that in trying to preserve 90 degree angles, it ends up giving a skewed sense of distance, which is evident in the reported distances from Washington, D.C. to Kabul, Afghanistan. Conformal maps are the type of maps most commonly used in activities, such as navigation.

These two maps are examples of Equidistant Map Projections. They are the Conic Equidistant and Sinusoidal Equidistant Projections. These projections preserve distance on the map between any two points. They take into account the curvature of the earth, and therefore, represent distance quite accurately, as shown by the distances reported between Washington, D.C. and Kabul, Afghanistan.

These two map projections (Mollweide Equal Area and Cylindrical Equal Area) are examples of Equal Area map projections. This means that they do a very good job of preserving area on a map. Equal Area map projections are useful when determining the area of two features, such as wetlands. Having an accurate representation of a wetlands area is crucial for many aspects concerning it, such as conservation policy.

Overall, maps can differ greatly depending on the map projection that is used. This is because the earth is not a perfect sphere and so in preserving one aspect, we distort another. That means that different map projections will be useful for different uses.