GeoTAX is most useful for identifying small-area geography. Small-area geography denotes the finest levels of the Census geographic units listed in the previous section, ranging from the county (the primary political division of a state) to the block (the smallest statistical region available, generally containing only 18 to 22 households).
Small-area geography was created by the Census Bureau for the purpose of accurate statistical reporting. With this goal in mind, the following have been important considerations in the development of the current census small-area geographic system:
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Designed to have relatively stable boundaries
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Designed to represent smaller populations with greater specificity than other geographic systems
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Originally defined by local committees to reflect some continuity of population characteristics.
For the purposes of this product, there are several major "small-area" units for sectoring the United States:
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County — Divisions within a state
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Metropolitan Statistical Area (MSA) — One or more counties that have a certain level of social and economic interaction with a large population nucleus (such as a city or town).
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Core Based Statistical Area (CBSA) — The county or counties or equivalent entities associated with at least one core (urbanized area or urban cluster) of at least 10,000 population, plus adjacent counties having a high degree of social and economic integration with the core as measured through commuting ties with the counties associated with the core.
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Places — A geographic area defined on the basis of population criteria that vary by state. Or, an area recognized as significant because it is located in an incorporated municipality. Places are mutually exclusive.
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Minor Civil Divisions (MCDs)/Census County Divisions (CCDs) — Primary sub-county political or administrative divisions
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Census Tract/Block Numbering Area (BNA) — Divisions of a county
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Block Group — Further divisions of the census tract/BNA.
Each of the small-area units listed above is described in more detail on the following pages.