In Census Bureau data products, geographic entities usually are presented in a hierarchical arrangement or as an inventory listing.
A hierarchical geographic presentation shows the geographic entities in a superior/subordinate structure. This structure is derived from the legal, administrative, or areal relationships of the entities. The hierarchical structure is depicted in report tables by means of indentation. For computer-readable media, the hierarchy is shown in the descriptive name applied to a summary level, with the hierarchy in order separated by hyphens. An example of hierarchical presentation is the census geographic hierarchy consisting of census block, within block group, within census tract, within place, within county subdivision, within county, within state. Graphically, this is shown as:
Place (or part)
Census tract (or part)
Block group (or part)
The Standard Hierarchy of Census Geographic Entities [PDF] presents this information as a series of nesting relationships. For example, a line joining the lower-level entity place and the higher-level entity state means that a place cannot cross a state boundary; a line linking census tract and county means that a census tract cannot cross a county line; and so forth. There is no implied hierarchy between different line tracks; for example, census tract nests within county, but it may cross a county subdivision boundary even though county subdivision also nests within county.
An inventory presentation of geographic entities is one in which all entities of the same type are shown in alphabetical, code, or geographic sequence, without reference to their hierarchical relationships. Generally, an inventory presentation shows totals for entities that may be split in a hierarchical presentation, such as place, census tract, or block group. An example of a series of inventory presentations is state, followed by all the counties in that state, followed by all the places in that state. Graphically, this is shown as:
Exceptions to the standard hierarchical presentation occur for entities that do not necessarily nest within states, most notably American Indian, Alaska Native, and Native Hawaiian areas and core based statistical areas.
American Indian, Alaska Native, and Native Hawaiian Area (AIANNHA) Hierarchy
Because federally recognized American Indian areas can cross state lines, a separate American Indian, Alaska Native, and Native Hawaiian area (AIANNHA) hierarchy exists for these areas. For instance, the following American Indian entities can cross state lines: federally recognized American Indian reservations and/or off-reservation trust lands, tribal subdivisions, tribal designated statistical areas, tribal census tracts, and tribal block groups. National summary data for American Indian reservations or statistical areas may be presented as an alphabetical listing of names followed by the state portions of each area. Also, a tribal census tract or tribal block group may be located in more than one state or county. Data for tribal census tracts and tribal block groups are presented only in Census Bureau products utilizing the AIANNHA hierarchy and are not present in products utilizing the standard census geographic hierarchy.
The Hierarchy of American Indian, Alaska Native, and Native Hawaiian Areas[PDF] shows geographic relationships among geographic entities in the AIANNHA hierarchy. It does not show the geographic levels county, county subdivision, and place, among others, because AIANNHAs do not necessarily nest within them.