By Ether Data
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Offshore islands

Global

Small islands belonging to a mainland admin region are geometrically disjoint (multipolygon parts) and can be dropped by fillers that assume a single contiguous ring.

Detection

MultiPolygon feature where one or more parts have a centroid far outside the bounding box of the largest part.

Mitigation

  • Iterate all multipolygon parts explicitly, never just the largest
  • Verify per-part cell coverage in QA rather than aggregate area only

Affected conversions

  • PolygonH3 (intersects)
  • Admin polygonsH3 (max-overlap partition)
  • Admin polygonsH3 (weighted crosswalk)