A geographic division is an area defined clearly with legal or commonly recognized borders, which may fit into a parent-child relationship with larger or smaller geographic divisions. Generally a geographic division at the smallest level fits into one at the next smallest level, and so on, although a child area may overlap two parent areas in some cases (e.g. a country may be on two continents).

The borders can arise from law or from common geographic recognition. The area can relate to larger and smaller divisions without requiring every boundary to nest perfectly.

A cross-boundary case can place a smaller division within more than one broader area. The defined extent remains meaningful even where the usual pattern of geographic containment has an exception.

Four properties describe such a division, and they answer different questions. The region group is the tier it occupies, the same everywhere on earth, which is what lets a district in one country be compared with a district in another. The region type is the local word for it, a label with no structure behind it, so one word can occur on several tiers and one tier carries a different word in each country. The division basis is the kind of division it came from, whether a council, a statistics office, a land register or common speech drew it. The division sort ranks divisions that cover the same ground, because a place is often divided several ways at once.