An important part of spatial analysis is the representation of the data and how it relates to the real-world. For some analyses being able to accurately calculate distances and measurements is extremely important especially when the outcome is based on the distances between features or objects. This brings us to the topic for today projections. The purpose is not to go into the details but to provide you with enough information so that you can make an informed decision about what projection to use.
A map projection is a systematic transformation of the latitude and longitude of a location into locations on a plane. There are bucket loads of projections some of which distort the earth more than others. Different map projections exist in order to preserve some properties at the expense of other properties. ALL map projections distort the surface of the earth one way or another. Depending on the purpose of the map needed or the type of analysis needed, some distortions are more acceptable than others.
To help in determining what projection is needed here is a summary of the projection, properties of the projection and some common uses.
| Projection | Properties | Common Uses |
| Conformal | Preserves local shapes and angles | weather maps, topographic maps, navigation charts |
| Equal Area | Preserves areas | Thematic maps (land use) |
| Equidistant | Preserves distance from one or two specified points to all other points on the map | Maps of airline distances, costs or charges based on straight-line distances. |
| Azimuthal | All directions are true from a single specified point (usually the center) to all other points on the map | Navigation and route planning maps |
If you are using GPS information. This data is usually provided in latitude / longitude, but it is wise to check the owner’s manuals for details.
For additional information about projections see the info provided by the USGS.
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