Lab 5 - Projections in ArcGIS

Map projections allow us to view the world on flat, portable surfaces like a piece of paper, and on the computer screen using digital map data. Since the Earth is more or less a 3-D sphere, projections are key in translating the world into a more practical 2-D format. The Earth can be represented at various scales depending on the type of projection. Consequently, the three-dimensional Earth can be observed and analyzed from different perspectives and in appropriate detail.

Perils of map projections predominantly lie in their inevitable distortions. Map projections using different developable surfaces, such as planes, cones, and cylinders, produce various distortions. As we transfer information from the real world to a virtual map, projections distort the shape, area, distance, and/or direction of the Earth. For example, the maps below show significant variance in distance between Washington, D.C. and Kabul, Afghanistan based on the projections used. Thus, mapmakers and readers must be wary of the map’s scale and purpose when choosing an appropriate projection.

Map projections offer a much more transportable, useful means of transferring geographic information compared to physical globes, and moreover, allow the user to cater to specific mapping tasks. One can choose from hundreds of projections to best serve the scale and function of the map, whether it is for a small-scale map of the entire world or a detailed area of a city. If one is looking to calculate the true distance between Washington, D.C. and Kabul, for instance, one should use an equidistant map. There is a map projection to serve almost any criteria. Ultimately, the user has the power to decide and can even use multiple ones to map the same area as I did below.

In this week’s lab we explored three classifications of map projections - equidistant, conformal, and equal area – based on distortion properties. The equidistant projections – Equidistant Conic and Sinusoidal – both maintain distances from the center or along specified lines. I mapped two conformal projections – Mercator and Stereographic – that preserve angular relationships and the shapes of local areas. Lastly, the two equal area projections – Mollweide and Bonne – maintain the same proportional areas as the real world and exhibit true directions from the map’s center. Exploring these various map projections and their characteristic distortions heightened my geographic understanding and helped me appreciate the importance of educated mapmaking and reading.