The Built Complexes and Districts hierarchy contains terms for coherent groupings of built works and for parts of settlements. Complexes are defined as aggregations of buildings, other structures, and open spaces, often multifunctional and more extensive, and usually shaped over a longer period of time by more participants than single built works. Districts are defined as delineated or perceived components of settlements that are more extensive and less architectonic than built complexes. These areas are likely to be defined by socio-economic characteristics or topographic features, by a sameness of the built works they encompass, or by administratively created boundaries. Relation to other hierarchies: Terms for public transit systems (e.g., "streetcar systems") are found in the Object Groupings and Systems hierarchy. Terms for types of road (e.g., "highways," "streets") are fund in the open spaces portion of the Open Spaces and Site Elements hierarchy. Terms for constituent parts of roads (e.g., "bus lanes," "curbs") are found in the Components hierarchy.
