For this week's lab, we compared the distance of two cities Washington D.C. and Kabul between different map projections in order to see how much these differences differed depending on the map projection. We utilized two equal area projections, two equidistant projections and two conformal projections. As you can see when referring to these different map projections, the appearance, shape, and distortions of each of the maps differ depending on the the type of map projection (conformal, equidistant or equal area) it is and even the specific map projection the map is made from. For example, the equidistant conic looks significantly different than the Hotine, both in the representation of the entire earth and the way the continents are arranged on the map. This is significant for map makers and map users because it is an obvious display of how map projections can make earth's surface look distinctly different and can impact the way we utilize maps. Taking into consideration which projections distort and preserve certain features (area, distance, shape, etc.) is essential to creating an appropriate map. These maps also show that there is always a distortion, no matter what type of map projection that you use, so knowing the map projection you use is critical and significant for keeping all the datums that you use consistent.
The perils of map projections mainly stem from the distortions that are inherent in each type of map projection. As you can see below each of the projections, the distance measured between the two cities mapped (Washington D.C. and Kabul) on each projection is very inconsistent. None of the measured distances match up between any of the projections. These measurements differ by more than a thousand miles when comparing the equidistant conic and the azimuthal equidistant maps (which preserve distance)! These data inconsistencies can become a big issue if you are collaborating with someone else and both parties are using different map projections. It can also be an issue when inputting data from one projection into a map with a different map projection.
The potential of map projections include highlighting certain properties and preserving specific factors in order to get the three dimensional surface of the earth on a two dimensional map. Also, map projection potential includes having the earth portrayed on a flat surface. As it's impossible to get earth on a two dimensional surface without distortion, having different types of map projections are extremely important because different map projections will allow the map user and anyone analyzing the map to have confidence in certain aspects of the map projection and compensate for a lack of accuracy in other aspects of the map created from particular map projections. For example, map users, cartographers and map analyzers can have confidence in the sinusoidal (an equal area map) to accurately portray equal area, but they will understand that these maps may not be completely accurate in terms of distance or shape. The variety of these different projections allow cartographers to choose different projections that will appropriately fit their needs.
Overall, projections are extremely important in cartography and ArcGIS use. Projections are essential to create a three dimensional image on a two dimensional surfaced. Despite their distortions, the variety of projections allow cartographers and GIS users to choose the appropriate projections that will enable the map to portray what they need. It is extremely important that people using GIS understand which projection they are using so they can compensate for and understand the distortions and inaccuracies inherent within that map projection.
The perils of map projections mainly stem from the distortions that are inherent in each type of map projection. As you can see below each of the projections, the distance measured between the two cities mapped (Washington D.C. and Kabul) on each projection is very inconsistent. None of the measured distances match up between any of the projections. These measurements differ by more than a thousand miles when comparing the equidistant conic and the azimuthal equidistant maps (which preserve distance)! These data inconsistencies can become a big issue if you are collaborating with someone else and both parties are using different map projections. It can also be an issue when inputting data from one projection into a map with a different map projection.
The potential of map projections include highlighting certain properties and preserving specific factors in order to get the three dimensional surface of the earth on a two dimensional map. Also, map projection potential includes having the earth portrayed on a flat surface. As it's impossible to get earth on a two dimensional surface without distortion, having different types of map projections are extremely important because different map projections will allow the map user and anyone analyzing the map to have confidence in certain aspects of the map projection and compensate for a lack of accuracy in other aspects of the map created from particular map projections. For example, map users, cartographers and map analyzers can have confidence in the sinusoidal (an equal area map) to accurately portray equal area, but they will understand that these maps may not be completely accurate in terms of distance or shape. The variety of these different projections allow cartographers to choose different projections that will appropriately fit their needs.
Overall, projections are extremely important in cartography and ArcGIS use. Projections are essential to create a three dimensional image on a two dimensional surfaced. Despite their distortions, the variety of projections allow cartographers and GIS users to choose the appropriate projections that will enable the map to portray what they need. It is extremely important that people using GIS understand which projection they are using so they can compensate for and understand the distortions and inaccuracies inherent within that map projection.
Equal-Area Projections: Eckert VI & Sinusoidal
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| Eckert VI Distance: 7,551 miles.
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| Equidistant Conic Distance: 7,118 miles.
Conformal Projections: Hotine & Stereographic |
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| Hotine Distance: 7,053 miles. |
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| Stereographic Distance: 9,814 miles. |
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