Lab #5 Projections

Map projections represent the physical world as a two dimensional image.  Projection always creates some level of distortion.  There are three main types of projections, 1.)Equal Area  2.)Equidistant 3.)Conformal.  Equal Area projection as the name implies preserves area.  Equidistant projection preserves distance, and Conformal projection preserves angles.

Equal Area projections, are noted as preserving area accurately, however measurements of distance are unreliable.  An example would be the Cylindrical Equal Area projection, which represents the areas of continents closely to reality. A fallout of Equal Area projections is that latitudinal distances are greatly distorted, especially towards the poles.  These distortions can also be seen in the Hammer-Aitoff Equal Area projection, which represents area of continents accurately but distorts length and angles of the continents.  This is why the distance between Washington, D.C. and Kabul is misrepresented in Equal Area projections.



Cylindrical Equal Area
Distance from Washington D.C. to Kabul, Afghanistan = 10,100 miles

Hammer-Aitoff Equal Area
Distance from Washington D.C. to Kabul, Afghanistan = 8,400 miles

Equidistant projections are useful in measuring distance accurately, but have other shortcomings.  The Cylindrical Equidistant projection produces continent shapes that are distorted longitudinally.  Additionally, the size of Antarctica has been greatly increased in this projection.  In the Sinusoidal Equidistant projection, continent shapes are greatly distorted.  This type of projection is the best choice when measuring long distance on a global scale.


Cylindrical Equidistant
Distance from Washington D.C. to Kabul, Afghanistan = 5,070 miles

Sinusoidal Equidistant
Distance from Washington D.C. to Kabul, Afghanistan = 8,104 miles 

Conformal projections represent the angles and outline of continents well but lack distance and area accuracy. The Gall Stereographic projections is a type of conformal projection which carries these features.  In this projection areas are greatly distorted, especially toward the poles.  The distance between Washington, D.C. and Kabul is also misrepresented in this type, therefore it is a poor choice for distance data.  It is more useful as a directional navigation reference.  A modified mercator projection, called a Miller Cylindrical, is another type of Conformal projection which is used for maritime navigation purposes.

Gall Stereographic
Distance from Washington D.C. to Kabul, Afghanistan = 7,182 miles

 Miller Cylindrical
Distance from Washington D.C. to Kabul, Afghanistan = 10,076 miles

The thing to learn from this lab exercise is when using GIS, it is important to consider projection differences and to note these differences to choose an appropriate map projection.