What makes a polygon invalid?
A polygon must follow structural rules: rings need enough coordinates, boundaries must close, holes need to sit inside an outer shell and edges should not cross in ways that create ambiguous interiors.
| Problem | What it means | Usual response |
|---|---|---|
| Ring not closed | The final coordinate does not match the first. | Close the ring when that reflects the intended boundary. |
| Too few distinct points | The ring cannot form an area. | Redraw or remove the collapsed part. |
| Self-intersection | Boundary segments cross each other. | Inspect the crossing and reshape or polygonise carefully. |
| Hole outside shell | An inner ring is not contained by its outer boundary. | Move, remove or reclassify the ring. |
| Overlapping MultiPolygon parts | Parts occupy the same area. | Union the parts or correct the source geometry. |
Validation workflow
- Choose a file or the current project. Open the validator from the More menu.
- Review every reported issue. Distinguish structural errors from warnings that require human judgement.
- Apply safe fixes selectively. Automatic closure of a nearly closed ring may be straightforward; changing a self-intersection can alter the intended area.
- Compare before and after. Inspect shape, area, holes and feature count.
- Download or import the fixed result. Keep the original file until the repaired output has been independently checked.
Geometry repair is not always lossless. A technically valid result can still be geographically wrong. For cadastral, legal, safety-critical or operational boundaries, verify against the authoritative source.
Preventing invalid polygons
- Avoid dragging vertices across non-adjacent edges.
- Do not create extremely small spikes or duplicate points.
- Inspect holes after merge, clip, erase and split operations.
- Validate again after format conversion.
- Test the exported file in its destination system.
Ready to work on your file?
Open the editor, import your geometry and use the relevant operation from the toolbar or More menu.
Open the editor