Census Tract Boundaries 2010

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人口普查区（census tracts）是县或同类行政单元下属的小型且相对固定的统计分区。地方参与方会在每一轮十年一度的人口普查前，作为美国人口普查局（Census Bureau）公众参与统计区域规划（PSAP）项目的一部分，对人口普查区进行审核与更新。当不存在地方参与方，或地方、部落政府拒绝参与时，由美国人口普查局自行完成人口普查区的更新工作。人口普查区的主要设立宗旨，是为十年人口普查数据的展示提供一套稳定的地理单元集合。4-24 人口普查区通常的人口规模为1200至8000人，最优人口规模为4000人。其空间尺度差异极大，具体取决于聚居地的人口密度。理想状态下，人口普查区的边界应长期保持稳定，以便于不同次人口普查间的统计数据对比。然而，因高速公路建设、新开发项目等引发的街道格局物理变化，可能需要对普查区边界进行修订。此外，人口规模的显著变化也可能导致普查区被拆分或合并。人口普查区的边界通常遵循可见且可识别的地理特征。普查区边界也可依照法定边界划定——例如，在部分州内遵循民政分区（Minor Civil Divisions，MCD）或已设建制地区的边界，以建立普查区与行政单元之间的对应关系，这类行政边界在两次人口普查间通常保持稳定。在标准普查地理层级体系中，州界与县界始终作为人口普查区的边界。在极少数情况下，人口普查区可能包含非连片区域。这类非连片区域通常出现在普查区与本身即为非连片的法定行政单元全部或部分范围重合的场景中。