The TIGER/Line Files are shapefiles and related database files (.dbf)
that 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 File 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.