This GIS layer contains the geographical boundaries of the 2020 census blocks for Loudoun County, Virginia. The 2020 Census block boundaries were used for statistical data collection and tabulation purposes for the 2020 Decennial Census. Census blocks are the smallest geographic area for publishing data from the decennial Census. The geographical area covered by this geographic feature class is generally very small in densely settled areas, for instance one city block. In sparsely settled areas they may cover several square miles. Census blocks nest within every 2020 Census geographic area (i.e. block groups, tracts, census designated places, and local, state, and federal election districts). This nesting of blocks allows Census Bureau statistical data to be tabulated to the appropriate geographic areas by aggregating the block data up. Census blocks are uniquely numbered within census tracts, with the blocks valid range being 1 to 9999 with leading zeros added (i.e. 0001, 0023) when necessary to create a four digit unique identifier. This 2010 Census block layer is based on the U.S. Census Bureau Census 2020 TIGER/Line files. The boundaries are an extract of aerial photography and cartographic information, such as roads and streams, from the Loudoun County GIS system. Census Blocks are bounded on all sides by visible features, such as roads, streams, lakes, power lines, and railroad tracks, and/or by non-visible boundaries such as town and county boundaries, and short line-of-sight extensions of streets and roads.