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 Blocks are statistical areas bounded on all sides by visible features, such as streets, roads, streams, and railroad tracks, and/or by nonvisible
           boundaries such as city, town, township, and county limits, and short line-of-sight extensions of streets and roads.  Census blocks are relatively small
           in area; for example, a block in a city bounded by streets.  However, census blocks in remote areas are often large and irregular and may even be many
           square miles in area.  A common misunderstanding is that data users think census blocks are used geographically to build all other census geographic
           areas, rather all other census geographic areas are updated and then used as the primary constraints, along with roads and water features, to delineate
           the tabulation blocks.  As a result, all 2010 Census blocks nest within every other 2010 Census geographic area, so that Census Bureau statistical data
           can be tabulated at the block level and aggregated up to the appropriate geographic areas.  Census blocks cover all territory in the United States,
           Puerto Rico, and the Island Areas (American Samoa, Guam, the Commonwealth of the Northern Mariana Islands, and the U.S. Virgin Islands).  Blocks are the
           smallest geographic areas for which the Census Bureau publishes data from the decennial census.  A block may consist of one or more faces.