How can I convert features of a layer from POLYGON to MULTIPOLYGON? I know how to do that using the postgis function ST_Multi but how could I do to same thing for a layer in QGIS?
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Seems to be a comment please expand on what your are asking– Mapperz ♦Commented May 13, 2015 at 14:57
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2 Answers
If you want to do it based on a field, you can do this in QGIS from the menu: Vector --> Geometry Tools --> Collect Geometries (requires at least two poylgons to share an attribute that you specify).
There is a more direct equivalent to ST_Multi in OGR. I didn't find a way to access this specific OGR functionality through QGIS, but that could be done using GDAL/OGR like this ogr2ogr -nlt MULTIPOLYGON multipolygon_output.shp polygon_input.shp More details on -nlt switch are available on the ogr2ogr page.
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I mamanged to do it with GDAL/OGR as you said, thanks. Let's see if someone can find a solution to this directly in QGIS.– EgidiCommented May 14, 2015 at 13:17
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While still waiting for the simple QGIS solution you can have a look at how it goes with OpenJUMP through the right-click menu:
