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I have 4 vector shapefile that I would like to join/merge, without worrying about attributes.
Here are the shapefiles.
I would like to do an union and a spatial dissolve, but everytime I do a dissolve after "PUP" and "PRG" layers union, I got an error about wrong geometries and the output layer is empty.
I validated layers geometry with no errors (at least is what QGIS tells me).

Am I missing out something?

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version of QGIS, GRASS? I would also check geometry with GRASS. –  Vladimir Nov 24 '12 at 16:27
    
QGIS 1.8.0 GRASS 6.4 on a Mac –  sanzoghenzo Nov 25 '12 at 12:50
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1 Answer

up vote 1 down vote accepted

While doing spatial joins in QGIS you have to make sure that all your layers are in the same projection! Otherwise there is a high chance of wrong outputs.

In your example data the shapes PUP and PRG have no correct set CRS projection, while the other shapes are all in ETRS89/ETRS-TM32.

-> Reproject them by saving them with the correct CRS (right-click on layer -> save as with selected ETRS89/ETRS-TM32 projection). -> Then load in the reprojected layers and merge them via the mmqgis function merge layers or through the function in the QGIS vector menu.

As soon as you have one single shape, you'll find the dissolve function in the vector menu.

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ok, I'm an idiot. I thought "they have the same projection, even if it's not specified, it should work..." It worked quite well. Thankyou so much! –  sanzoghenzo Nov 25 '12 at 13:00
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