2020 Census Block Groups
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A Block Group usually covers a contiguous area. Each census tract contains at least one BG, and BGs are uniquely numbered within the census tract. Within the standard census geography hierarchy, BGs never cross state, county, or census tract boundaries but may cross the boundaries of any other geographic entity. There are little more number of Census Block Groups within Los Angeles County in 2020 Census TIGER/Line Shapefiles, compared in 2010. BGs are generally define to contain between 600 to 3,000 people and 240 and 1,200 housing units. BGs are the smallest geographic unit for which the Census Bureau tabulates sample data. Created/Updated: Updated on September 2023, to merged Long Beach Breakwater land-based block group silver polygons into bigger block group 9903000 as per 2022 TIGER Line Shapefiles, and to update Santa Catalina Islands and San Clemente Islands block group boundary based on DPW City boundaries (except 5990002 tract in Avalon). Updated on Sep 2022 and Dec 2022, to align tract boundary along city boundaries. Created on March 2021. How This Data is Created? This geographic file was downloaded from Census Bureau website: https://www2.census.gov/geo/tiger/TIGER2020PL/STATE/06_CALIFORNIA/06037/ on February, 2021 and customized for LA County. Data Fields: 1. BG20 (BLKGRPCE20): 7 digit census tracts and block group number, 2. CT20 (TRACTCE20): 6-digit census tract number, 3. Label (NAMELSAD20): Block group number label
普查街区组（Block Group，BG）通常覆盖一片连续的区域。每个人口普查片区（census tract）至少包含一个普查街区组，且各BG在所属普查片区内拥有唯一编号。在标准的普查地理层级体系中，BG不会跨越州、县或人口普查片区的边界，但可跨越其他任意地理实体的边界。相较于2010年，2020年人口普查TIGER/Line形状文件（TIGER/Line Shapefiles）中洛杉矶县的普查街区组数量略有增加。 普查街区组通常被设定为包含600至3000名居民以及240至1200套住房的地理单元。BG是美国人口普查局（Census Bureau）编制抽样统计数据的最小地理单元。 创建与更新记录：2023年9月更新：依据2022年TIGER/Line形状文件，将长滩防波堤陆上普查街区组的面状多边形合并至更大的街区组9903000；同时依据公共工程局（Department of Public Works, DPW）的城市边界（阿瓦隆市的5990002普查片区除外），更新圣卡塔利娜岛与圣克莱门特岛的普查街区组边界。2022年9月及12月更新：将人口普查片区边界与城市边界对齐。2021年3月首次创建。 数据制作方式：该地理数据文件于2021年2月从美国人口普查局官网下载（下载地址：https://www2.census.gov/geo/tiger/TIGER2020PL/STATE/06_CALIFORNIA/06037/），并针对洛杉矶县（LA County）完成定制化处理。 数据字段： 1. BG20 (BLKGRPCE20)：7位编码的人口普查片区与街区组编号 2. CT20 (TRACTCE20)：6位编码的人口普查片区编号 3. 标签（NAMELSAD20）：普查街区组编号标签
