Equal Area Projections
Distance between Washington, D.C. and Kabul, Afghanistan
Mollweide Equal Area Projection: 7,910 miles
Bonne Equal Area Projection: 6,787 miles
Equidistant Projections
Distance between Washington, D.C. and Kabul, Afghanistan
Azimuthal Equidistant Projection: 8,419 miles
Sinusoidal Equidistant Projection: 8,095 miles
Conformal Projections
Distance between Washington, D.C. and Kabul, Afghanistan
Mercator Conformal Projection: 10,074 miles
Stereographic Conformal Projection: 9,911 miles
Map projections are essential to the functional use of geographic information.The earth is not flat, yet it is necessary to be able to observe angles, distances, and areas in more useful two-dimensional formats. Because the ideal functions of a map vary per situation, there is a wide variety of projections used in mapmaking. Three commonly used types of projections are equal area, equidistant, and conformal.
Equal area projections preserve area, and it is represented with equally-sized areas on the globe between the meridians and parallels on the map. This form of representation is important when showing distributions or other items where it is critically important to show equal area. The Mollweide projection is a common form of equal area map, and is often used when it is more important to observe distributions over global area than show accurate shape. The Bonne equal area projection is a less modernly used pseudoconical map. Pseudoconical maps are similar to conical projections except that their meridians are not constrained to straight lines. The distances recorded between Washington, D.C. and Kabul, Afghanistan on the Bonne and the Mollweide exhibit great a difference. Equal area projections are found to be not useful for preserving distance.
Equidistant projections preserve distances extending from a center reference point. This is extremely useful for situations where distance is needed to be calculated from a starting location, such as with air travel from take-off or when conducting seismic work. It is important to acknowledge that reference points are essential for determining distance in this form of projection. Therefore, different types of equidistant projections will display a variation of distances when measuring between the same two locations on the globe. However, if the reference points are similarly located you may close measurements. The azimuthal equidistant projection and the sinusoidal projection are good examples of similar measurements. The sinusoidal only preserves distances along parallels so slight variation will most likely be observed.
Conformal projections preserve local angles. The mercator projection is one of the most common types that is widely used and observed. In the past, the mercator has been useful for navigation. However, this type of projection greatly distorts size and shape of large objects. This occurs because the scale naturally increases as it displays areas from the equator to the north and south pole. Stereographic projections also preserve angles, but are more concerned with preserving the shape of circles on the globe. Distance is often skewed, but depending on reference point close measurements might be observed between two conformal projections. The mercator and the stereographic produced similar but, by no means, accurate measurements.
