2020 Census Tracts

The TIGER/Line shapefiles and related database files (.dbf) are an extract of selected geographic and cartographic information from the U.S. Census Bureau's Master Address File / Topologically Integrated Geographic Encoding and Referencing (MAF/TIGER) Database (MTDB). The MTDB represents a seamless national file with no overlaps or gaps between parts, however, each TIGER/Line shapefile is designed to stand alone as an independent data set, or they can be combined to cover the entire nation. Census tracts are small, relatively permanent statistical subdivisions of a county or equivalent entity, and were defined by local participants as part of the 2020 Census Participant Statistical Areas Program. The Census Bureau delineated the census tracts in situations where no local participant existed or where all the potential participants declined to participate. The primary purpose of census tracts is to provide a stable set of geographic units for the presentation of census data and comparison back to previous decennial censuses. Census tracts generally have a population size between 1,200 and 8,000 people, with an optimum size of 4,000 people. When first delineated, census tracts were designed to be homogeneous with respect to population characteristics, economic status, and living conditions. The spatial size of census tracts varies widely depending on the density of settlement. Physical changes in street patterns caused by highway construction, new development, and so forth, may require boundary revisions. In addition, census tracts occasionally are split due to population growth, or combined as a result of substantial population decline. Census tract boundaries generally follow visible and identifiable features. They may follow legal boundaries such as minor civil division (MCD) or incorporated place boundaries in some States and situations 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. For the 2020 Census, the census tract code range of 9400 through 9499 was enforced for census tracts that include a majority American Indian population according to Census 2010 data and/or their area was primarily covered by federally recognized American Indian reservations and/or off-reservation trust lands; the code range 9800 through 9899 was enforced for those census tracts that contained little or no population and represented a relatively large special land use area such as a National Park, military installation, or a business/industrial park; and the code range 9900 through 9998 was enforced for those census tracts that contained only water area.TIGER/Line形状文件（TIGER/Line shapefiles）及关联数据库文件（.dbf）是从美国人口普查局的主地址文件/拓扑集成地理编码与参照系统（Master Address File / Topologically Integrated Geographic Encoding and Referencing，简称MAF/TIGER数据库，MTDB）中提取的精选地理与制图信息子集。MAF/TIGER数据库为无缝全国数据集，各组成部分间无重叠与间隙，但各TIGER/Line形状文件均可作为独立数据集单独使用，亦可组合覆盖全美全域。 人口普查地段（Census tracts）是县或等效行政单元下辖的小型、相对固定的统计分区，由本地参与方作为2020年人口普查参与方统计区域计划的一部分划定。若无本地参与方，或所有潜在参与方均拒绝参与，则由美国人口普查局负责划定该类地段。人口普查地段的核心功能是提供一套稳定的地理单元，用于呈现人口普查数据，并与历次十年一次的人口普查数据开展对比。其人口规模通常介于1200至8000人，最优规模为4000人。最初划定时，人口普查地段的设计目标是在人口特征、经济状况与居住条件方面保持同质性。其空间范围因聚居密度差异存在显著差异。 公路建设、新开发项目等引发的街道格局变更，可能需要对地段边界进行修订。此外，人口增长可能导致人口普查地段被拆分，而人口大幅减少则可能导致地段被合并。人口普查地段的边界通常遵循可见且可识别的地物。在部分州及特定场景中，边界可遵循法律边界，如小型民事分区（Minor Civil Division, MCD）或建制居民点边界，以建立人口普查地段与政府单元的对应关系——这类政府边界在两次人口普查周期内通常保持稳定。在标准人口普查地理层级体系中，州界与县界始终属于人口普查地段的边界范畴。 在极少数情形下，人口普查地段可能由非连片区域组成。这类非连片区域通常出现在普查地段与本身即为非连片的法律实体全部或部分范围重合的场景中。 针对2020年人口普查，三类人口普查地段被指定了专属代码范围：其一，根据2010年人口普查数据，人口以美国印第安人为主，或辖区主要位于联邦认可的美国印第安人保留地及保留地外信托土地上的地段，适用9400至9499的代码范围；其二，人口极少或无人口、且代表大型特殊土地用途区域（如国家公园、军事设施或商业/工业园区）的地段，适用9800至9899的代码范围；其三，仅包含水域区域的地段，适用9900至9998的代码范围。