Distortion

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A distortion is the alteration of the original shape (or other characteristic) of an object, image, sound, waveform or other form of information or representation. Distortion is usually unwanted. In some fields, distortion is desirable, such as electric guitar (where distortion is often induced purposely with the amplifier or other electronic effect to achieve a unique sound). The slight distortion of analog tapes and vacuum tubes is considered pleasing in certain situations. The addition of noise or other extraneous signals (hum, interference) is not considered to be distortion,^{[citation needed]} though the effects of distortion are sometimes considered noise.

In Geographical Information Systems, we often try to portray the world on a flat map so that we can see, analyze, find, and use the geography of the world. This is difficult to do because we are trying to make a round object flat. If you deflate a basketball can you lay it flat on the ground? This is a difficult task to accomplish without cutting lines into the outer layers of the ball, even then you cannot fit all the cut pieces into a square flat shape. The same things happen when we try to represent (or project) the three dimensional geography of the world on a flat surface.

[edit] Map projections

In cartography, a distortion is the misrepresentation of the area or shape of a feature. There are no map projections that can maintain a perfect scale throughout the entire projection because they are taking a sphereoid and forcing it onto a flat surface. There are four main types of distortion that come from map projections: distance, direction, shape and area. The Mercator projection, for example, distorts Greenland because of its high latitude, in the sense that its shape and size are not the same as those on a globe. Another example is in cylindrical projections. With projections the distortion is minimal at the lines of tangency, or the line along which the projection and the surface of the earth intersect. The further from those lines you get, the more distortion appears in the projection. Different projections are better at minimizing different typed of distortion. For example, conformal conic projections mostly preserve shape, equidistant projections preserve distance and equal area projections preserve area.

[edit] See also

• Aliasing
• Image warping
• Intermodulation distortion
• Lossy compression
• Minimum Resolvable Contrast
• Quantization distortion

[edit] References

This article includes a list of references, related reading or external links, but its sources remain unclear because it lacks inline citations. Please improve this article by introducing more precise citations where appropriate.

 This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C" (in support of MIL-STD-188).

• Riesterer, J.; Introduction to Topographic Maps, Geospatial Training and Analysis Cooperative, Department of Geosciences, Idaho State University. Accessed 27 September 2011.
• Map Projection Distortion, Department of Geography, Hunter College of the City of New York University. Accessed 27 September 2011.
• Dana, Peter H., Map Projection Overview, University of Colorado at Boulder Web site. Accessed 27 September 2011.