In QGIS, one polygon feature resulted from merger of several adjacent polygons. This one new polygon feature has a single line through it that I would like to eliminate. When hovering over individual nodes in edit mode a balloon displays polygon number, ring number, and vertex number and in this case the adjacent parts of the new polygon have polygon numbers 0 or 1. How do I combine the polygon parts of this new single polygon feature?
So, I suggest my cartographic approach to solving your problem and its name sounds like “wedge” or “insertion” (I'm not sure that Google will translate it correctly, though ...)
Initial data: two broken adjacent polygons.
1) Polygon into points, for which run the tool: Vector-> Geometry Processing-> Extract vertices;
2) Edit the points, as shown in my screenshot below, i.e. leave the adjacent points unchanged (4 - two each next to numbers 1 and 2);
3) Run the Vector-> Geometry-processing tool on points-> Delaunay Triangulation ...
see screenshot below;
4) Select the "wedge", copy it and paste in edit mode into your working layer;
5) Combine the three parts of your polygons into one by running the Vector-> Geoprocessing-> Merge by Basis ... tool, replace it in the original layer
and everything seems to be ...