A polygon boundary sounds simple, but the GeoJSON standard and TRACES apply several structural rules to it. Each exists so the plot area is unambiguous. Here is every rule that applies to an EUDR plot polygon and what it means in practice.
The rules
| Rule | What it means |
|---|---|
| Closed rings | The last coordinate of a ring must equal the first, so the boundary returns to its start. An open ring is rejected. |
| At least four positions | A ring needs a minimum of four positions (three corners plus the closing repeat) to enclose an area. |
| No self-intersection | The boundary must not cross itself. A self-intersecting ring has an undefined interior and is invalid. |
| Right-hand winding | Exterior rings run counter-clockwise, holes run clockwise. This is the GeoJSON right-hand rule, and TRACES can be strict about it. |
| No duplicate vertices | Repeated consecutive points can make a ring invalid and should be removed. |
| WGS84 coordinates | Longitude and latitude in degrees, longitude first, at about 6 decimal places. |
Which of these can be fixed automatically
Most of them, safely: closing an open ring, correcting winding, removing duplicate vertices, and repairing a self-intersection are deterministic repairs. A ring with fewer than four positions cannot be invented into a valid area, so that one is reported for you to correct.
MultiPolygon plots
A plot split into separate parcels can be a MultiPolygon, where each part follows the same ring rules. The same checks apply to every ring of every part.
Common questions
What does closing a ring mean?
The first and last coordinate of the ring must be identical, so the boundary forms a closed loop. If they differ, the ring is open and rejected.
What is the right-hand winding rule?
Exterior rings should be counter-clockwise and interior holes clockwise. The fixer corrects winding automatically.
Check your polygons against every rule
Validate free and let the fixer close rings, correct winding, and repair invalid polygons for you.
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