special region
A bounded geographic place that does not fit ordinary geographic divisions because of its extent, distribution, or special purpose.
Special regions are any types of geographic places with defined borders which do not fit well within the hierarchy or geographic divisions. These are usually distinguished by one of the following: they are not properly nested in a hierarchy of regions between one level and another; they occur only occasionally and do not blanket a larger area by bordering each other; or they are created for special limited purposes and do not have full status as geographical "places".
The area can overlap ordinary divisions or sit between their usual levels without forming a complete additional tier. Its distinct boundary does not require all surrounding territory to have equivalent special regions.
A metropolitan area groups closely interacting urban places. Other special regions can arise from a different limited purpose or pattern of geographic recognition.