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I'm trying to delete all polygons with an area smaller than a certain give value. Is this possible in qgis?

The goal here is to delete all the islands off a map.

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3 Answers 3

up vote 4 down vote accepted

So I figured it out

  1. vector-> geometry tools->Export/Add geometry columns
  2. right click on the layer that you added the geometry columns and select query
  3. enter "AREA" > SOME VALUE and click ok
  4. right click on the the layer you just queried and choose save as and that is the final file
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If this solves your problem, can you mark it as "the answer"? –  BradHards Apr 12 '13 at 5:23
    
it says "You can accept your own answer tomorrow" –  null_radix Apr 12 '13 at 17:26
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don't forget to come back today and accept it then :-) –  iant Apr 15 '13 at 10:39

If you are looking to delete the polygons, then you will want to have an attribute with area. In an editing session, query the field where areas is less than 'X'. With the polygons selected, delete the records (red circle with the X). Save the editing session and stop the editing session. This will permanently delete the records from the file.

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An easy way if you have an area field in your attribute table is to just control click on the area field and sort ascending and drag and highlight all polygons you want to delete, you can try and avoid deleting landlocked small polygons with this method.

There's also probably a functionality similar to or the same as calculate geometry in ArcGIS which will generate the Area data and populate the fields of your attribute table with it.

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