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I'm learning how to use QGIS (v 1.8.0 "Lisboa") on Mac OS 10.6.8. My goal is to create a simple county map of Illinois using the base data shapefiles available from the Illinois Natural Resources Geospatial Data Clearinghouse.

Following workflow suggestions in another thread, I first checked "Enable 'on the fly' CRS transformation" in Project Properties.

Then I added the shapefile:

Illinois wide

I then changed the CRS in Project Properties to NAD83/Illinois (West) [EPSG code 26972] to get the desired look:

Illinois

So far so good. But after saving the QGIS file, closing it, then opening it again, I get a CRS error:

Transform error caught: forward transform of (0.000000, 0.000000)
PROJ.4: +proj=longlat +datum=WGS84 +no_defs +to +proj=tmerc +lat_0=36.66666666666666     
+lon_0=-90.16666666666667 +k=0.999941177 +x_0=700000 +y_0=0 +ellps=GRS80   
+towgs84=0,0,0,0,0,0,0 +units=m +no_defs
Error: latitude or longitude exceeded limits

How do I prevent this type of error?

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1 Answer

up vote 2 down vote accepted

Changing the CRS in layer properties is something different than reprojecting the data in the file. Your file still has +proj=longlat. You attempt to display 0°E/0°N (somewhere next to the coast of Nigeria) into the Illinois state plane, and that will not work.

Open the layer in longlat, and rightclick -> Save As ... into EPSG:29672 under a different name, and add the result to the canvas.

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Thanks for the answer, Andre. Just so I understand the terminology... Is this process of saving the layer with a different CRS considered a "re-projection"? Or am I confusing the terms? –  syncrasy Mar 6 '13 at 22:14
    
Yes, In QuantumGis the reprojection of vector data is made in the save as option. –  Gerardo Jimenez Mar 7 '13 at 5:08
    
You just have to make sure that you have no points in your lat/long file that can not be reprojected to NAD83 CRS systems because they are laying far apart from the US. You can look at your data in WGS84, catch and delete them. –  Andre Joost Mar 7 '13 at 6:47
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