Equal Area Map Projections
Equidistant Map Projections
The process of accurately transforming the spherical shape to flat surface, while preserving shape, size, distance, and area, has baffled cartographers and mathematicians a like for centuries. Since it is not possible to perfectly transform all points on a sphere to a flat surface while preserving all aspects of the image, various methods have been developed to accurately preserve characteristics of the sphere. These methods are called Map projections. These projections, named projections because early forms were created by projecting light from the inside of a sphere, are tools to create accurate flat maps based on the spherical earth. Since carrying a globe, or globes for that matter, around with you is not an option, projections have been the key in creating accurate flat maps. Projections are only able to preserve a number of spatial characteristics while no one projection can preserve them all at once. Three main classifications of map projections are the Conformal, Equidistant, and Equal Area projections. Each of these projections has its own advantages and disadvantages which are clearly displayed through the maps above.
These three projection categories, Conformal, Equidistant, and Equal Area, each have their own unique advantages. Conformal maps allow for shape to be preserved while making longitudinal and latitudinal gridlines to intersect at right angles. These examples of conformal maps can be seen in the Mercator and Gall Stereographic maps above. Equal Area maps preserve area as suggested by their name. The whole of the Equal Area map has the same equivalent area as the Earth as a whole. This element of Equal Area projections is well illustrated by the Mollweide projection map shown above. Equidistant maps show true distances along certain designated lines or from the center of the projection outward (or visa versa) but not between points that are not near the center. The Equidistant Conic projection above shows how true distance from Africa to Australia could not be easily measured using this map. These map projection categories have their key uses but also could be the wrong choice for certain location data depending on the elements of interest.
Though one category may work very well in one instance, it is certainly not guaranteed to work well next time. Conformal maps, though very good at preserving angles between gridlines, distort sizes of areas significantly. This is well demonstrated by the size of Antarctica in the Mercator projection above. Equal Area maps also have disadvantages in contrast with their ability to preserve area well. Equal Area maps can never offer the preservation of gridline angles while still sustaining accurate area. As shown above when comparing the Mercator projection to the Equal Area projections, you can see how the gridlines look nothing alike. Equidistant projections have trouble, as mentioned before, with measuring distances of locations outside of the center, or along the lines, designated. Another disadvantage to these types of maps is that they can never offer true distances while still preserving equal areas. This is illustrated well by the distortion in area within the Plate Carree projection above. These types of disadvantages come with all projections and are a necessary evil to properly presenting map data.
Map projections are a very important concept to be understood when working with or even reading any maps. This knowledge allows the map observer and creator to better understand how to decipher and construct accurate features. This understanding of both advantages and disadvantages to projections allows for a better realization of which projection is the best and most accurate choice for a two dimensional map.
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