In QGIS I have a polygon SHP layer. The layer contains rings. I am reshaping the polygon layer by cutting away large areas of the polygons. When cutting away a part of the polygon that contains a ring, what happens to the ring? Is it completely removed?
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1Can you insert an image graphic to support your question?– artwork21Commented Nov 30, 2015 at 13:08
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1 Answer
I don't think anything happen to the ring as the Reshape tool does not allow rings to be cut if more than one polygon is crossed. The documentation regarding reshaping features might be helpful in describing this in more detail. The following quote is taken from the link:
You can reshape line and polygon features using the Reshape Features icon on the toolbar. It replaces the line or polygon part from the first to the last intersection with the original line. With polygons, this can sometimes lead to unintended results. It is mainly useful to replace smaller parts of a polygon, not for major overhauls, and the reshape line is not allowed to cross several polygon rings, as this would generate an invalid polygon.
If you want to reshape rings then make sure you only draw a line covering the ring itself. There is also the Delete Ring tool if you want to completely remove them.
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1Re. the "delete ring" tool: My reason for asking the question in the first place, was that the tool does not work. What I ended up doing was using the "clip" tool to clip a polygon around the ring. This splits the polygon in two. Then deleting the polygon with the ring inside.– KalleCommented Dec 1, 2015 at 13:00
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@Kalle - I think there have been some issues with this feature in various QGIS versions, there was a post which asked this. That is a good alternative you mentioned. Another is to > select the polygon with the ring > delete the ring with Delete Ring > create a small ring inside the deleted ring using Fill Ring > merge the new ring and the polygon using Merge selected features.– JosephCommented Dec 1, 2015 at 13:13