Self-intersection
When a polygon boundary crosses itself (a bow-tie shape), often making it invalid.
Category: Topology
Definition (expanded)
Self-intersections frequently cause union and difference failures or strange results. Many tools fix this via a small buffer(0)-style clean, polygonization, or snapping. The right fix depends on what shape you actually intended.
Related terms
Valid geometryA geometry that follows topological rules (closed rings, no self-intersections, properly nested holes, etc.).BufferCreates a new geometry expanded (or shrunk) by a distance around the input geometry.DifferenceAn operation that subtracts one geometry from another (A minus B).Make validA repair step that converts invalid polygons into valid geometry, often by splitting or reshaping boundaries.SnappingAdjusting vertices to line up within a distance tolerance, often used to clean boundaries before overlay operations.