Lab 5: Projections

The idea of map projections is a method for putting the sphere into two dimensional space. No matter how you do it these maps will be distorted. Generally, there are only really three ways to do try to do this. Your maps are either conformal, equidistant, or equal area. Conformal maps include projections like the Mercator or the North Pole Stereographic. They are intended to preserve angular relationships which is great in some situations (like navigation) and not as good in others. Equidistant projections like the Sinusoidal and the Plate Carree featured above intend to preserve distances between the origin and everything else on the map. Finally, equal area projections are meant to preserve the sizes of geographic features.

Conformal maps like the Mercator are probably the most common kind of map that you see in everyday life. It is used in classrooms, for reference, and for exploration. Its great because its relatively easy to make and read. However, it does distort the area closer to the poles. That’s why you see places like Greenland seeming so much larger than they really are. As a kid I thought Alaska was bigger than Mexico as a result of this distortion. Equidistant maps have a lot of positive features as well. For example, it’s the kind of map that you would want to use if you were measuring distance between points like Washington D.C. and Kabul for example. However, this only holds true if the points are of similar latitude in the Sinusoidal. If the straight line between the points is more diagonal then this kind of projection is more of a problem and you might want to use something like the Plate Carree which preserves distance along all latitudes. Equal Area maps like the Goode’s Homolosine projection is the best for maintaining the correct area of land masses. This way Greenland isn’t any bigger than it should be. However, it isn’t as good for comparing land features because it’s hard to represent the whole world as a rectangle.

Knowing the benefits and pitfalls of each of the types of projections, it becomes clear that there is no clear correct choice for maps. It is best to just choose your projection based on the circumstances and what your trying to convey. Nothing is going to preserve the correct comparative distance, shape, or area. Below are examples of each type of projection:



Conformal Maps

1: Mercator Projection: 10,112 miles
2: North Pole Stereographic Projection: 7,617 miles

Equidistant Mapping Projections

3: Sinusoidal: 8,098 miles
4: Plate Carree: 10,109 miles

Equal Area Maps

5: Lambert Azimuthal Equal Area: 6,806 miles
6: Goode’s Homolosine (Land): 9,986 miles