Self-intersection (polygon error)

Why does it matter?

Geospatial software assumes valid geometries. A self-intersecting polygon can produce wrong areas, fail overlap checks with forest maps, or be rejected when uploaded. In EUDR evidence, invalid geometries weaken the credibility of the whole dataset.

How is it detected?

Validity checks based on the OGC Simple Features rules test whether:

• the ring is closed;
• edges only meet at shared vertices;
• there are no spikes or zero-area sections;
• holes lie inside the exterior ring.

Open-source geometry libraries provide these checks and repair functions.

How is it fixed?

1. Detect invalid polygons at capture time, on the device, so the agent can re-walk the boundary while still in the field.
2. Apply automatic repair for small errors, such as a tiny loop from GPS drift.
3. Compare the repaired area to the declared area and to the original shape.
4. Flag large differences for field verification or re-mapping with imagery.

Common pitfalls

• Repairing silently, without recording that geometry changed, which breaks the audit trail.
• Validating only at export, weeks after the field visit.
• Treating a self-intersection as a formatting issue rather than a data quality signal.

Farmer1st validates polygons at capture and repairs or flags errors through its geo and polygons service.