In QGIS I have simplified a layer. At the end of the simplification process (using GRASS v.generalize), my final layer "lost" a polygon: see white space in image:

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How can I recreate a polygon which would fill that empty space? I have tried using "Fill Ring" but that did not work.

  • Go back to GRASS and add a centroid in that empty boundary. – Micha Jun 10 '15 at 11:27
  • Hi. To simplify my original layer I have used the GRASS Command in the Processing Toolbox. Using QGIS, how do I add a centroid? – Michele Jun 10 '15 at 11:45

You can digitize the border of the polygon. Just make sure of

a) Set the proper snapping options at settings/snapping options

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for this case I will snap on the vertex of the existing polygons with a tolerance of 15 pixels. More important, I set that I do not want intersection of new polygons (avoid intersections)

Once you have set that, select your layer, put it in edition mode. The following images are an example

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This is what you have

Now I digitize intersections on every boundary of the existing polygons

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Notice that I invaded the existing polygons, but I define an intersection for every common border. Also notice that the island is completely coverd with the new polygon (the red one)

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Since you defined that you did not want intersections of new polygons, these are erased, keeping perfect common borders and also your island.Save your editions and that should do it.

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In this image I erased the island to show that the polygon that I digitized preserved the Island as a single feature. Notice that the digitized polygon contains the island "hole".

hope it helps

  • Normally this should work even without snapping on those shared vertices but by simply digitizing through all adjacent polygons. I even avoid to snap on anything, but keep a distance to those borders so I can be sure I do not snap on some wrong vertex producing tiny slivers etc. – Bernd V. Jun 10 '15 at 22:02

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