I'm editing a polygon layer in QGIS that contains several small polygons within larger polygons. To save time drawing the larger (encompassing) polygons, I'm using the "avoid intersections" option, along with "enable topological editing" and "enable snapping on intersection" options on. When I complete drawing a large polygon, all polygons render properly (i.e., the smaller polygons within the larger polygon are avoided/preserved as individual features, with proper topology as expected). However, once I save my edits, the larger polygon covers the smaller polygons. Is this an issue anyone else has encountered? If so, what is the solution?

I have tried exporting the shapefile (save as--> new name). That does not work.

The attached photos illustrate more clearly what I am trying to describe. The image above shows the smaller polygons that were drawn first. The image below shows the polygon I have drawn on top of them (colored yellow), which covers them upon saving the edits.

Thank you! enter image description here

  • Perhaps this tool is not planned for polygons which are totally included in another. Make a test with a big polygon and a shall one that a) is totally inside b) overlaps partially. What should work is to digitize big polygon to own layer and bore holes to that by calculating the difference (big one - union of smalls). – user30184 May 6 '17 at 8:26

First I suspected your small polygons were several sets of multipart polygons, so just made a quick test.

The tested multipart object is shown as two yellow squares (FID=1). It turned out, however, mutipart polygon had no influence.

enter image description here

What I had to do was to remove self-intersected feature (lower left on the figure) to make avoid intersections work.

So... can you check Geometry errors on the small polygons?

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.