Census Block Group Boundaries 2020

Standard block groups are clusters of blocks within the same census tract that have the same first digit of their 4-character census block number (e.g., Blocks 3001, 3002, 3003 to 3999 in census tract 1210.02 belong to block group 3). Current block groups do not always maintain these same block number to block group relationships due to boundary and feature changes that occur throughout the decade. For example, block 3001 might move due to a change in the census tract boundary. Even if the block is no longer in block group 3, the block number (3001) will not change. However, the GEOID for that block, identifying block group 3, would remain the same in the attribute information in the TIGER/Line shapefiles because block GEOIDs are always built using the decennial geographic codes. Block groups delineated for the 2020 Census generally contain 600 to 3,000 people. Local participants delineated most block groups as part of the Census Bureau's PSAP. The Census Bureau delineated block groups only where a local or tribal government declined to participate or where the Census Bureau could not identify a potential local participant. A block group usually covers a contiguous area. Each census tract contains one or more block groups and block groups have unique numbers within census tract. Within the standard census geographic hierarchy, block groups never cross county or census tract boundaries, but may cross the boundaries of county subdivisions, places, urban areas, voting districts, congressional districts, and AIANNH areas. Block groups have a valid range of zero (0) through nine (9). Block groups beginning with a zero generally are in coastal and Great Lakes water and territorial seas. Rather than extending a census tract boundary into the Great Lakes or out to the 3-mile territorial sea limit, the Census Bureau delineated some census tract boundaries along the shoreline or just offshore.标准街区组（standard block groups）是指同一普查区（census tract）内，其四字符普查街区（census block）编号首位数字相同的街区集群。例如，普查区1210.02内的3001、3002、3003至3999号普查街区隶属于3号街区组。由于十年间发生的边界与要素变更，当前的街区组未必始终维持原有的街区编号与街区组对应关系。例如，3001号普查街区可能因普查区边界调整发生移位。即便该普查街区不再隶属于3号街区组，其街区编号（3001）也不会发生改变。但在TIGER/Line形状文件（TIGER/Line shapefiles）的属性信息中，该普查街区用于标识3号街区组的地理标识符（GEOID）仍将保持不变，因为普查街区的地理标识符始终基于十年一次的地理编码生成。2020年人口普查划定的街区组通常涵盖600至3000名居民。多数街区组由当地参与者作为美国人口普查局（Census Bureau）公共安全应答点（PSAP）的参与方完成划定。仅在当地或部落政府拒绝参与，或普查局无法确认潜在当地参与者的情况下，普查局才会自行划定街区组。街区组通常覆盖连片区域。每个普查区包含一个或多个街区组，且街区组在所属普查区内拥有唯一编号。在标准普查地理层级体系中，街区组绝不会跨越县或普查区的边界，但可能跨越县分区、建制地、城区、投票区、国会选区以及美国印第安、阿拉斯加原住民与夏威夷原住民地区（AIANNH）的边界。街区组的编号有效范围为0至9。以0开头的街区组通常位于沿海区域、五大湖水域及领海范围内。美国人口普查局并未将普查区边界延伸至五大湖或3英里领海界限处，而是沿海岸线或近岸海域划定了部分普查区边界。