Census Tract Boundaries 2000

Census tracts are small and relatively permanent statistical subdivisions of a county or equivalent entity. Local participants review and update census tracts prior to each decennial census as part of the Census Bureau’s PSAP. The Census Bureau updates census tracts in situations where no local participant existed or where local or tribal governments declined to participate. The primary purpose of census tracts is to provide a stable set of geographic units for the presentation of decennial census data. 4-24 Census tracts generally have a population size of 1,200 to 8,000 people with an optimum size of 4,000 people. The spatial size of census tracts varies widely depending on the density of settlement. Ideally, census tract boundaries remain stable over time to facilitate statistical comparisons from census to census. However, physical changes in street patterns caused by highway construction, new development, and so forth, may require boundary revisions. In addition, significant changes in population may result in splitting or combining census tracts. Census tract boundaries generally follow visible and identifiable features. Census tract boundaries may follow legal boundaries (e.g., MCD or incorporated place boundaries in some states to allow for census tract-to-governmental unit relationships where the governmental boundaries tend to remain unchanged between censuses). State and county boundaries always are census tract boundaries in the standard census geographic hierarchy. In a few rare instances, a census tract may consist of noncontiguous areas. These noncontiguous areas may occur where the census tracts are coextensive with all or parts of legal entities that are themselves noncontiguous人口普查街区（census tract）是县或同类行政单元划定的小型且相对固定的统计分区。作为美国人口普查局（Census Bureau）PSAP项目的组成部分，地方参与方需在每一轮十年一次人口普查开展前，对人口普查街区进行审核与更新。若不存在地方参与方，或地方、部落政府拒绝参与，美国人口普查局将自行更新人口普查街区。 人口普查街区的核心用途是提供一套稳定的地理单元，用于呈现十年一次人口普查的统计数据。4-24 人口普查街区的人口规模通常介于1200至8000人之间，最优规模为4000人。人口普查街区的空间跨度差异显著，取决于定居点的人口密度。 理想状态下，人口普查街区的边界应长期保持稳定，以便实现不同轮次人口普查间的统计对比。但公路建设、新开发项目等引发的街道格局物理变更，可能需要对街区边界进行修订。此外，人口规模的显著变化可能导致人口普查街区被拆分或合并。 人口普查街区的边界通常以可见且可识别的地物为参照。人口普查街区的边界可遵循法定边界（例如，部分州的民政分区（MCD）或建制区域的边界，以便建立人口普查街区与行政单元的对应关系，这类行政边界在两次人口普查之间通常保持稳定）。在标准普查地理层级中，州界与县界始终作为人口普查街区的边界。 在极少数情况下，人口普查街区可能由不相连的区域组成。当人口普查街区与本身即为不相连的法定单元的全部或部分区域重合时，便会出现这类不相连的街区区域。