Is my understanding correct, namely that two polygons touching at a common point cannot be merged because the result would be a self-intersecting polygon? I know there are dozens of Q&A threads on self-intersecting polygons and I’ve looked through them. This post: Detecting invalid polygons (self-intersecting or touching) seems to indicate merging 2 polygons with a single common point into one would create a self-intersecting polygon, and would thus be invalid. Likewise, the answer to this post Is it possible to have self intersecting polygons in shapefile? suggests such a geometry could not be stored in a shapefile. However, this post seems to indicate it is possible to accomplish it: Combining corner-touching polygons into a single feature.
The reason I ask is that this post: Merging polygons that share one vertex (node neighbors) using ArcGIS Desktop? suggests the user is trying to do exactly that and encountering errors. I’m posting it as a separate question here because my comment on that last post (poorly framed as a subsidiary question) was deemed invalid. Apologies in advance if I have not done the linking correctly in this question or I’ve deviated from protocol by referring to a deleted comment. I’m trying to improve my understanding of valid and invalid geometry.