Projection/ Coordinate Systems in Quantum GIS

Projection is very important when creating maps.  They can create distorted maps or any analysis of the information can be incorrect.

 

To set the projection for an entire project

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The box below will open up.

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‘On the fly projection’ in quantum means that the as the layers for the project are added they will be projected in whatever coordinate reference system you have chosen. This does not actually change the coordinate system of

the layer just how they are projected.

 

For this example on the fly is not selected. When this option is turned off the layers will project as is and you can also change the project units.

 

 

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When on the fly is enable these options will gray out and then you will be allowed to set the projection for the project.

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Keep in mind you can not change the units as these will be set by the CRS you choose.

 

To change the CRS of a layer it needs to be saved with a new CRS.

 

Right click on your layer>Save As

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You have three options for the CRS. You can either save it with the CRS it is in (Layer CRS)

You can set it to the project (Project CRS)

Or you can choose a new CRS from the list (Selected CRS)

 

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To see the CRS of your layer there are a few options.

Right click on the layer>Properties>Metadata Tab and then look under Layer Spatial Reference System.

 

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Or find where you have your layers saved

Right click on the .prj and choose open. If it prompts you to choose a program from the list/installed programs  select Notepad. This only needs to be done once.  Just be sure to check always use for this

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And it opens a notepad with the projection and CRS information.

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