Lab 5 - Map Projections in ArcGIS

The perfect map would be an exact representation of the real world; this would occur by having the ratio of the distances between any two points be the same on the map and in real life. However, this representation is not possible when portraying the spheroid world on a flat surface. There are three map projections that preserve some aspect of real life: equal area, equidistant, and conformal projections. In each map, I measured the distance from Washington, D.C. to Kabul in miles. The most accurate distance is using the Geographic Coordinate Systems, and is measured at around 6932 miles.

Equal area projections, as shown in the Goode’s Homolosine Land map and the Mollweide map, preserve area. In other words, the area on land is represented through the same ratio of area on the map. The Goode’s Homolosine Land map reported a distance of 9986 miles from Washington, D.C. to Kabul, while the Mollweide map reported a distance of 7926 miles. The Good Homolosine Land map’s distance is over 3000 miles off from the actual distance and the Mollweide map’s distance is just under 1000 miles off. Since the area is preserved and not the distance, the distance reported is clearly exaggerated in equal area projections.

Conformal projections, as shown in the Stereographic and Mercator maps, preserve shape and angles. Conformal projections are mainly used to represent a local area. To be considered conformal, the angles at any two lines on the map are the same as the angles in real life. The Stereographic map reported a distance of 9878 miles from Washington, D.C. to Kabul and the Mercator map reported a distance of 10,112 miles. Both of these distances are around 3000 miles more than the GCS distance, demonstrating that distance is dramatically changed when a map is focused solely on angles.

Equidistant projections, as shown in the Azimuthal Equidistant map and the Equidistant Conic map, preserve distance among a reference line. The Azimuthal Equidistant map reported a distance of 8341 miles between Washington, D.C. while the Equidistant Conic map reported a distance of 6972 miles. Clearly, the map projection that shows the most accurate distance between the two locations is the Equidistant Conic. However, the distance is not exactly what GCS reports because the equidistance aspect of the map only refers to the distance between two specific points on a reference line.

With the dramatic differences in distance between two locations shown above, it is obvious that choosing a map projection should not be taken lightly. Your map projection should depend on what you are representing on your map, from a distance-accurate city map to a shape-accurate world map.