I digitized already two areas, bordering each other on one side. Then I realized that more detail was needed!

What do you suggest as a fast way to do so?

  • Adding each time new dots/vertices takes so much time.
  • But, adding a new polygon and merge both (as I used to do for a not bordering polygon) does not seem that easy in this case.
  • Using the split feature causes an invalid area which I cannot merge with the other area afterwards.
  • In the snapping options set the Avoid intersection to that layer. Then, when digitalizing the second polygon, near the border, just draw simple lines inside the first polygon. In the end QGIS will erase the overlapping part. – Alexandre Neto Apr 21 '13 at 0:01
  • Do you have topological editing turned on? – Simbamangu Apr 21 '13 at 4:14
  • @AlexandreNeto, my secondon polygon has already been drawn. Its just I want to get more detail into it, which I can do by adding new intersection points on the common line and move them to the right place. But that would take too much time compared to splitting. – Sironsse Apr 21 '13 at 19:37
  • @Simbamangu, I tried both, turned on and turned of. Do you mean for the split feature? – Sironsse Apr 21 '13 at 19:40
  • Maybe another approach, isolate both polygons in a shapefile and merge them (give polygon 2 attributes). Make sure you have no holes in the resulting polygon. Use polygons to lines on polygon 1 to convert it to lines. Then use union to cut your bigger polygon in two, or use Difference to erase polygon 1 area. – Alexandre Neto Apr 22 '13 at 8:37

The Reshape Feature Tool enter image description here can be helpful for this job.

Draw the new common border of the polygons (here in red color): enter image description here

  • That's what I was looking for!! The button was always there but I didn't think about it to use it this way. – Sironsse Apr 22 '13 at 8:29

I'm assuming the boundary you need to edit is the common boundary between the two objects?

  1. Merge the two polygons - if they were digitised using topological editing then there should be no gaps or overlap between them;
  2. Split the polygons with a new line.

You'll lose the attributes of one of the features.

After (1) check that the merged area is clean with no holes or weird geometry.

  • Great idea, but for my purpose, the reshape feature tool seems more useful (the polygons are a tangle, also having common boundaries at other locations). – Sironsse Apr 22 '13 at 8:27

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