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

Polygon → H3 (intersects) expansive
Admin polygons → H3 (max-overlap partition) approximate
Admin polygons → H3 (weighted crosswalk) weighted