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<br /> <br />7 <br />Definition of Terms - Geographies <br />Neighborhood: In this report, “neighborhoods” are approximated by <br />tracts.6 Tracts are statistical geographic units defined by the U.S. Census <br />Bureau for the purposes of disseminating data. In the Bay Area, tracts <br />contain on average 4,500 residents. Nearly all Bay Area jurisdictions <br />contain at least two census tracts, with larger jurisdictions containing <br />dozens of tracts. <br />Jurisdiction: Jurisdiction is used to refer to the 109 cities, towns, and <br />unincorporated county areas that are members of ABAG. Though not all <br />ABAG jurisdictions are cities, this report also uses the term “city” <br />interchangeably with “jurisdiction” in some places. <br />Region: The region is the nine-county San Francisco Bay Area, which is <br />comprised of Alameda County, Contra Costa County, Marin County, <br />Napa County, San Francisco County, San Mateo County, Santa Clara <br />County, Solano County, and Sonoma County. <br /> <br />6 Throughout this report, neighborhood level segregation measures are calculated using census tract data. <br />However, the racial dot maps in Figure 1 and Figure 5 use data from census blocks, while the income group dot <br />maps in Figure 8 and Figure 12 use data from census block groups. These maps use data derived from a smaller <br />geographic scale to better show spatial differences in where different groups live. Census block groups are <br />subdivisions of census tracts, and census blocks are subdivisions of block groups. In the Bay Area, block groups <br />contain on average 1,500 people, while census blocks contain on average 95 people.