FeatureID is the unique identifier for every boundary object in the dataset. There are two situations in which a FeatureID value would be duplicated:
- In the Administrative Boundaries extract, there are some cases where very large polygons (consisting of 500,000 or more nodes) are split into multiple polygons to provide compatibility with some popular databases. In such instances, the unique identifier is maintained, and the ID is duplicated and assigned to the split polygons.
- Also in the Administrative Boundaries extract, where part of a lower-level boundary intersects a higher-level boundary, the object may be split into multiple polygons so that both nest within the higher-level feature. The split polygons will maintain the original FeatureID value in this case.
Note that while FeatureID values are unique, they are not currently persistent. Changes for FeatureID values in each release are published in the ChangeID report.