ArcMap Projections

Above: Conformal World Map Projections illustrating distance from Washington D.C. to Kabul.


Above: Equal-Area World Map Projections illustrating distance from Washington D.C. to Kabul.




Above: Equidistant World Map Projections illustrating distance from Washington D.C. to Kabul.

Map projections help us represent 3-dimensional objects on to a planar surface. Being able to represent the Earth, which is a sphere, without any distortion at any level is impossible. Map projections allow for the most appropriate representation of the Earth, depending on the specific needs of the location information the map is trying to portray. Conformal projections are made to preserve angles - shape is preserved locally and meridians and parallels intersect at right angles; equal-area maps preserve area - mapped areas have the same proportional relationship to the areas on the Earth that they represent; and equidistant maps preserve distances.

There is no single map projection that can represent the Earth without any distortion. The reason there are so many different projections is to illustrate location for different purposes. A conformal map, such as the Mercator Projection shown above, would not be used to appropriately illustrate the distance from Washington D.C. to Kabul, Afghanistan. A more appropriate map to more accurately illustrate the actual distance would be an Equidistant map, such as the Equidistant Conic Projection, also shown above. Each projection is made to be appropriate for different uses, so it is important to use a projection that is accurate for the purpose of the map.

The two Conformal Projections I used above are Gall Stereographic and Mercator, which are commonly used for navigation. They represent the Earth with constant lines, that intersect at 90 degree angles, therefore direction is easier to follow. Mercator projection distorts the size and shape of objects and the scale increases from the equator to the poles. This causes the land masses at the poles to look much bigger than the land masses closer to the equator. The Equal Area Projections that I used are the Bonne and Sinusoidal Projections. These two preserve areal relationships of the different land masses. The real life ratios are maintained and illustrated as they are on Earth. Distance and shape are compromised, and significant distortion occurs in these two areas. The last two maps are Equidistant, Plate Carree and Equidistant Conic Projections. These maps are good for measuring distances accurately in relation to real life distances on Earth.

The approximate distance from D.C. to Kabul was measure for each map, and the one that came closest to the actual distance was the Equidistant Conic Projection. It is important to use projections that will most accurately represent the property that is being studied. If the wrong projection is used, shape, distance, angles, and area can be miscalculated.