2

New QGIS user, Brighton 2.6. I accidentally deleted an elongated (lots of "peninsulas" polygon that represents a stream-based habitat - two gaps on SW boundary and two on the northern boundary (leaving a small 'island' or floating polgyon.

It seems that one of the tools would allow quick closure of this area to draw back into as a record. There are four gaps at the formerly contiguous boundary, but if I could sketch a line across these gaps and close the area back in, that would be ideal.

edited image showing gap between polygons

Malamutte
  • 39
  • 7
  • This would be why we keep backups on a daily basis. Go back to your original data and copy/paste it in. If you don't have original data there are ways to 'construct' a new polygon.. I have answered a smilar question here http://gis.stackexchange.com/questions/101915/generating-polygons-with-streets-as-borders-using-qgis/101916#101916 that might help. Convert what you've got to lines http://docs.qgis.org/2.6/en/docs/user_manual/processing_algs/saga/shapes_lines/convertpolygonstolines.html fill gaps and delete lines that don't make the polygon you want then copy/paste/attribute. – Michael Stimson Mar 16 '15 at 22:47
  • @Michael Miles-Stimson - check out Vesanto's simple solution below. – Malamutte Mar 17 '15 at 12:27
  • Like the answer but that's still not an excuse to avoid having a backup policy, this isn't the only thing that can go wrong which a backup will save you from! Consider a basic copy/Zip before editing with a dated folder/zipfile. Hint: dates in YYYYMMDD(HHMM) will sort very well in explorer. Space is cheap, time is expensive! – Michael Stimson Mar 17 '15 at 21:29

1 Answers1

2

There should be a pretty simple solution to your issue. You can draw a polygon which will not overlap any other polygons in the same layer.

This is done by ticking the "Avoid Intersections" tick box in the snapping options (Settings> Snapping Options)

In QGIS 2.8 this is done through the "Advanced" mode, in 2,6 it should be the basic snapping options:

enter image description here

Then you can draw a large polygon, and snapping to your entrances as mentioned, but the polygon you draw will follow the boundary of the other polygons in the layer and not overlap them.

HeikkiVesanto
  • 16,433
  • 2
  • 46
  • 68
  • So do I create an entirely new polygon shapefile or use the "add part" tool or do I have to create a new polygon layer to abut and then merge or join to the this file? I am guessing this means the 'floating' shape in the center of this open area must get deleted then recreated. – Malamutte Mar 17 '15 at 11:48
  • You should create the new 'floating' polygon in the same layer (shapefile) as the other polygons. No need to do add part, since that would create a multipart polygon. – HeikkiVesanto Mar 17 '15 at 12:01
  • Oops. I used "add part" and filled in the gap but now have a new multipart polygon. Is there a quick way to split that back out? I looked it up here but can't find "explode multipart features". – Malamutte Mar 17 '15 at 12:07
  • 1
    You can through the menu: Vector> Geometry> Multipart to SinglePart but this will create a new shapefile.

    You can "Delete Part" and try again alternatively.

     – HeikkiVesanto Mar 17 '15 at 12:14
  • THIS WORKS. Easy & fast. – Malamutte Mar 17 '15 at 12:26