I have a layer that contains polygons that should be "topologically correct" if I understand that term correctly. The polygons should share vertices of adjacent polygons, allowing no gaps and no overlaps.
The trouble is that some were drawn manually it seems and I need to "fix" these not quite touching polygons. See the example below, showing part of two polygons that should be sharing a border but are not. What I would like is for the polygon containing vertices 1,2,3,4 to instead contain vertices 1,5,6,7,8,4 like the other one. This is a relatively simple example that could be fixed vertex by vertex using the "snapping" tool - adding additional vertices between 2 and 3, and snapping them to their counterparts. But some borders I would like to match up are much more complex where each may have hundreds of vertices that don't match but should, and I'd like to "snap" from a selected first point to a selected second point to replace all the vertices in one polygon to those in the other.
What I think I would like to do then is to select and "copy" in this example vertices 5, 6, 7, 8 from one polygon, then select the other polygon and select vertices 2, and 3, and "paste/replace" these two selected vertices with the vertices copied earlier. Of course I'd be copying a much more complex larger set of vertices.
Any ideas how to do this with QGIS? Any other tools come to mind?