natural division

A natural division is a division whose areas are set by the terrain: a valley, a basin, a range, an island or a group of them. Their edges follow watersheds, coastlines and ridgelines rather than a decision.

People name and use such areas and address them as places, while no authority defines their extent. Where a boundary is stored, it is derived from the landform, so two sources may draw it differently without either being wrong.

Where a municipality or region later adopted a landform's name for a unit of its own, that unit belongs to whichever division maintains it. The landform stays natural.