Lecture_05_projectnsdb

# Lecture_05_projectnsdb - Projections and Coordinate Systems...

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Projections and Coordinate Systems

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Since we can see only one side of the globe at once, a 2 dimensional representation of the earth can be useful to further our understanding about world relationships.

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Globes used to be made by pasting sections of maps onto a rigid sphere. These sections are called gores.
This illustrates how globes are made. The “undoing” of the globe does result in a world map. But it is excessively interrupted interrupted and does not have many of the properties of a map that we might desire.

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Map Projections A transformation of the spherical or ellipsoidal earth onto a flat map is called a map projection. The map projection can be onto a flat surface or a surface that can be made flat by cutting, such as a cylinder or a cone ( developable surface developable surface ). On a sunny day, your shadow is a projection of your 3D self onto the (nearly) 2D ground.
There are many projections and they have different characteristics All projections have some distortion The spatial pattern of distortion varies with different projections

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Masks derived from those worn by actors in ancient Greece. Plot them on a globe and analyze distortions on maps created using different projections
The main point here is not that any one of these is better than another, but that the choice of the choice of projection can make an projection can make an enormous difference enormous difference in whatever we do with geographic information. It follows, therefore, that projections are of fundamental importance to GIScience and are important to the educated use of GIS.

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Projections General problem is to transfer information from 3D to 2D The earth is 3D Which 2D do you use? Seems like an odd question but…
This is rather poorly drawn, since the point or lines of tangency are not really apparent, but the idea here is that if you had a translucent globe with a light inside it and you turned it on, it would cast a shadow on the developable surface (the plane, cylinder, or cone) and that shadow would be the projection of the spherical information onto that surface and it would be a projection of information from 3D to 2D.

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Developable Surfaces A developable surface is one that is either flat or can be can be made flat
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## This note was uploaded on 04/01/2012 for the course 044 005 taught by Professor Davidbennett during the Fall '11 term at University of Iowa.

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Lecture_05_projectnsdb - Projections and Coordinate Systems...

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