In this tutorial you will learn what valid means for a geometry and how to check validity in QGIS 3. You will also see how to fix validity problems and how to make a geometry simple.
Points and lines are always valid. A POLYGON is valid if the polygon boundary rings are simple (do not cross or self-touch). Because of this a polygon cannot have cut lines, spikes or loops. This implies that polygon holes must be represented as interior rings, rather than by the exterior ring self-touching (a so-called “inverted hole”).
Geometry has no anomalous geometric points, such as self-intersection or self-tangency.
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