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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
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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.

enter image description here

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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