Map Projections

Bonne: This equal-area projection has true scale along the central meridian and all parallels. The measured distance from Washington, DC to Kabul, Afghanistan is 6,731 miles. *

Cylindrical Equal Area: Lambert first described this equal-area projection in 1772. It is used infrequently.

The measured distance from Washington, DC to Kabul, Afghanistan is 10,108 miles.*

Azimuthal Equidistant: The most significant characteristic of this projection is that both distance and direction are accurate from the central point.

The measured distance from Washington, DC to Kabul, Afghanistan is 8,341 miles.*

Two Point Equidistant: This modified planar projection shows the true distance from either of two chosen points to any other point on a map.

The measured distance from Washington, DC to Kabul, Afghanistan is 6,649 miles.*

Hotine Oblique Mercator: This is an oblique rotation of the Mercator projection developed for conformal mapping of areas that do not follow a north–south or east–west orientation but are obliquely oriented.

The measured distance from Washington, DC to Kabul, Afghanistan is 9,629 miles.*

Stereographic: This azimuthal projection is conformal.

The measured distance from Washington, DC to Kabul, Afghanistan is 9,878 miles.*








***All measurements are planar.

 

When working with maps, projections are of usually of great importance. Map projections become negligible and irrelevant when working with extremely large scale (small area) maps. The smaller the map scale, the greater the importance of the projection. In all of the maps above, the scale is so small that different projections produce radically different measurements. For example, the measured distance from Washington DC, to Kabul, Afghanistan taken from the Two Point Equidistant map was 6,649 miles. From the Cylindrical Equal Area map, the distance measured was 10,108 miles. The measurements were taken from exactly the same points in exactly the same way. Yet, a difference in measurement of more than 3500 miles exists.

Different map projections are used for different purposes. The first pair of maps listed above are equal area projections. Equal area map projections are useful for a variety of purposes, but not for others. The Cylindrical Equal Area projection is very useful for gaining perspective. The mercator portrays the northern hemisphere, especially North America and Europe, as far more important than the land masses in the southern hemisphere. This is done by making North America and Europe look larger than they actually are relative to South America and Africa. When people see the Cylindrical Equal Area map for the first time, they are usually astonished. Certain projections, such as equal area, are very useful for gaining perspective.

Equidistant maps also have some very specific applications. Equidistant maps are point centric. This means that everything on the map will be the same distance from a certain point. For example, equidistant maps are currently being used to evaluate and analyze the North Korean missile crisis. These maps accurately depict the North Korean missile range. In the Azimuthal Equidistant projection, everything is the same distance from the center of the map. Additionally, in this projection, direction is also preserved in relation to the center. Preserving direction enables USGS to use this projection in the National Atlas of the United States of America.

Conformal maps, the last pair presented above, preserve size, direction, and spatial relations. Distances are very skewed in conformal projections. Above, measurements in the conformal maps differ by up to 3,000 miles. Most of the time, conformal projections are used when dealing with large scale maps. Small scale maps very rarely use conformal projections. In small scale applications, conformal maps are pretty to look at, but many times, are not useful mathematically. Despite this, they can still give the viewer a new perspective, aiding them in understanding the complex geographic relations of the world.

DAVID PHILLIPS
DAVID PHILLIPS
DAVID PHILLIPS