Cylindrical Projections
A Cylindrical Projection is one of the three ways that the spherical earth's coordinate system can be flattened (projected) on to a flat surface. This has been something that map makers have had to deal with throughout history. The term projection comes because of the physical analogy that a cylindrical projection would be taking a piece of paper and wrapping it around the globe in the shape of a cylinder. If their were a light in the globe that projected the lines of latitude and longitude on to the paper, when you laid the paper flat it would result in a cylindrical projection of the earth. Now with in this you can see various forms of cylindrical projections. There are those in which the map would have a line of tangency to the equator. There would also be Secant Cylindrical Projections. This would be if the paper cut through the surface so that their were two lines of tangency. This is done to try and minimize distortion. Understanding that we are working with a projection and what type of projection is vital to GIS. It is important to know that when dealing with GIS since in a GIS flat surfaces are some of the most valuable tools and forms worked on.[1]
There are multiple aspects of the cylindrical projection: 1-When it is tangent or secant to the equator it is termed regular, or normal. 2-When it is tangent or secant to a meridian it is termed transverse 3-When it is tangent or secant to another point on the globe it is oblique[2]
Regular Cylindrical projections include the Equirectangular Projection, the Mercator Projection, Lambert's Cylindrical Equal Area, Gall's Stereographic Cylindrical, and Miller cylindrical Projection. All of these projections have some similar characteristics. Their lines of latitude and longitude are parallel intersecting at ninety degrees, the meridians are equidistant, the scale along the equator is true and not distorted, they can each have the properties of equidistant, conformality, or equal area.[3]
The most widely know of the Regular projections and perhaps all Cylindrical Projections is the Equirectangular (Equidistant) Projection. It one of the oldest projections it is also the simplest. The parallels are equally spaced and it is the view we most often see when the image is created for the entire earth. It maintains correct distance between every point and the Equator. The shapes are distorted and also the area.[4]
The Transverse Cylindrical Projections include the Cassini Projection, Transverse Mercator, Transverse cylindrical Equal Area Projection, and Modified Transverse Mercator. The characteristics of a Transverse maps is that the line of tangency is rotated 90 degrees.[5]
The oblique Cylindrical Projections only consist of the Oblique Mercator. Here there is a 45 degree tilt of the regular cylinder so it gives it a different view.[6]
Sources
- ↑ Longley, Paul A. et al, Geographic Information Systems and Science(2005), 2nd Edition
- ↑ http://www.geography.hunter.cuny.edu/mp/cylind.html
- ↑ http://www.geography.hunter.cuny.edu/mp/cylind.html
- ↑ Longley, Paul A. et al, Geographic Information Systems and Science(2005), 2nd Edition
- ↑ http://www.geography.hunter.cuny.edu/mp/cylind.html
- ↑ http://www.geography.hunter.cuny.edu/mp/cylind.html
| Authors | Ben Hillam |
|---|---|
| Editors | Olaf Johnson, Teresa Gomez |
| BoK Topics | DN1, CV2, CVG |
| 311 Weeks | 7 |
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