Handling invalid geometries

Following a tutorial, I fixed a geometry error in a state boundary layer. While attempting to run the ‘topological coloring’ algorithm, I encountered an error. I ran vector geometry>check validity to find the root cause. There was a ring self-intersection, which happens when a geometry touches itself and generates a ring. I used the vertex tool to edit the layer and fixed the geometry.

Handling Invalid Geometries (QGIS3) — QGIS Tutorials and Tips