Self-intersecting polygon (figure eight): why the EUDR system rejects it

What the Information System does

It rejects the plot. The specification lists "shapes with crossing lines (like a figure eight)" among the shapes that "are not supported and will not be processed", and puts crossing lines first in its list of common file errors (GeoJSON File Description, Common errors 1). The Information System's own validation rules reject invalid geometries in general (Information System validation rules, Geolocation invalid geometry).

A broken example

{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "properties": {
        "ProducerCountry": "CI",
        "ProductionPlace": "Figure eight",
        "Area": 1.2
      },
      "geometry": {
        "type": "Polygon",
        "coordinates": [
          [
            [-5.123456, 6.123456],
            [-5.122456, 6.124456],
            [-5.122456, 6.123456],
            [-5.123456, 6.124456],
            [-5.123456, 6.123456]
          ]
        ]
      }
    }
  ]
}

What the checker reports for this file:

1. This polygon crosses itself between the sides starting at points 1 and 3. A shape like this has no single inside, so its area cannot be worked out., line 23, column 13

Fix it in EUDRplot

1. Open the file in the checker. Drop it on the checker. Every crossing is listed, and the map zooms to the exact point where two sides of the boundary cross.
2. Review the proposed repair. Choose Repair the crossing boundary. The repair rebuilds the boundary as one polygon for each loop of the figure eight, so no side crosses another. The before and after shapes are drawn on the map, dashed, with each plot's area in hectares before and after.
3. Accept only if the area is right. If the area changes by more than 2%, the repair is refused rather than applied: a change that large is a redraw, and it needs someone who knows the field. Otherwise choose Accept the change and apply; the change is recorded in the change log and the PDF report.
4. Check again and export. The file is re-checked straight away. Open Download and choose GeoJSON file, and, on a paid plan, the PDF check report if you need a record.

Fix it in QGIS

1. Find the crossing. Open the Processing Toolbox (Ctrl+Alt+T) and run Check validity on your layer with the GEOS method. The Error output layer marks each self-intersection with a point.
2. Repair the geometry. Run Fix geometries on the layer. A figure eight usually comes back as a MultiPolygon with one part for each loop, which the Information System accepts.
3. Compare the area. Set the project ellipsoid to WGS 84 (Project › Properties › General › Measurements), then add a field with the Field Calculator using $area / 10000 for hectares, and compare it with the original.
4. Export as GeoJSON. Right-click the layer › Export › Save Features As…, format GeoJSON, CRS EPSG:4326. Then check the result before uploading.