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I'm an experienced software developer -- but a GIS noob.

I have a shape file that I am trying to turn into a SVG map with Kartograph. When I try to run Kartograph I get this error:

ERROR 6: No translation for Lambert_Conformal_Conic to PROJ.4 format is known.

Because I don't want to delve into Kartograph, it seems like I need to reproject the shape file. The wikipedia page for shape files says that the .prj file describes the projection.

.prj — projection format; the coordinate system and projection information, a plain text file describing the projection using well-known text format

Can I just swap out the prj file to reproject the file? If so, where can I find a .prj file that will work to reproject the map so that Kartograph can turn it into an SVG?

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No, reprojection needs a source and a target. What you suggest would simply reassign the source metadata that is assumed to represent your data as they are. (Sometimes you need to do that but not here). It is perhaps a variant of that cs in PRJ that karto does not understand, but that is a different problem. Try spatialreference.org to explore the zoo –  mdsumner Feb 5 at 20:05
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up vote 9 down vote accepted

No, you can't just change the .prj file. The prj file defines the projection that is used for the geometries, so changing it would simply change how those geometries are displayed to the user.

Consider if you had a shapefile with points in lat/long. If you swapped the .prj file to redefine the projection to web mercator, all of your points would now be located in the Atlantic Ocean off the coast of Africa, since the coordinates would all be very close to 0,0!

You will have to reproject the shapefile to actually change the geometries to your new projection. See:

How to re-project shapefiles?

http://support.esri.com/en/knowledgebase/techarticles/detail/21447

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One thing: changing the PRJ file wouldn't make your shapefile invalid, it would still show up on your map, but your shapes would all be in the wrong place. If you're talking about two very different coordinate systems, like lat/long and State Plane, this error will be immediately noticeable. But if you're dealing with two similar coordinate systems, like State Plane in two different datums, the error may not be noticeable right away. So it's very important that the shapefile have the correct PRJ file attached to it. –  Dan C Feb 5 at 20:29
    
I guess that's semantics - I would consider a geometry that's in the wrong place to be invalid, regardless of how it got there. –  mwalker Feb 5 at 21:05
    
Right, I just wanted to emphasize that a shapefile could appear to work fine while actually displaying wrong information. –  Dan C Feb 5 at 21:06
    
Makes sense. I've edited my response for clarity. –  mwalker Feb 5 at 21:07
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