2020 Population By 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）及相关数据库文件（.dbf），是从美国人口普查局主地址文件/拓扑集成地理编码与参考数据库（Master Address File / Topologically Integrated Geographic Encoding and Referencing，MAF/TIGER数据库，简称MTDB）中提取的精选地理与制图信息数据集。MTDB为无缝全国数据集，各组成部分间无重叠或空隙，但每份TIGER/Line形状文件既可作为独立数据集单独使用，也可合并以覆盖全美范围。 人口普查片区（census tract）是县或等效行政单元的小型、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。 若不存在本地参与方，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人口普查片区。 人口普查片区的核心用途是提供一套稳定的地理单元，用于展示人口普查数据，并与过往十年一次的人口普查数据进行对比。 人口普查片区的人口规模通常介于1200至8000人之间，最优规模为4000人。 最初划定人口普查片区时，其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。 人口普查片区的空间范围因定居密度的差异而相差悬殊。 因高速公路建设、新开发项目等导致的街道格局实体变化，可能需要对人口普查片区的边界进行修订。 此外，人口普查片区偶尔会因人口增长而拆分，或因人口大幅减少而合并。 人口普查片区的边界通常遵循可见且可识别的地物。在部分州及场景下，边界可遵循法律边界，如县级以下民政分区（minor civil division, MCD）或建制居民点的边界，以确保人口普查片区与政府单元的对应关系——这类政府边界在两次人口普查之间通常保持稳定。 在标准人口普查地理层级中，州界与县界始终作为人口普查片区的边界。 在极少数情况下，人口普查片区可能包含非连片区域。 这类非连片区域通常出现在片区与全部或部分本身为非连片的法律实体范围重合的场景中。 针对2020年人口普查，下述代码范围被专门分配给特定类型的人口普查片区：代码段9400至9499，用于根据2010年人口普查数据判定为以美洲印第安人口为主，或区域主要由联邦认可的美洲印第安人保留地及/或保留地外信托土地覆盖的片区；代码段9800至9899，用于人口极少或无人口、且代表大型特殊土地利用区域（如国家公园、军事设施或工商园区）的片区；代码段9900至9998，用于仅包含水域区域的片区。