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 in, “Geographic Overview”). For example, there usually is both urban and rural territory within metropolitan and nonmetropolitan areas, there are urban places and rural places, urban parts of States and rural parts of States, and so forth. The boundaries of UAs can cross State and county boundaries, as well as the boundaries of county subdivisions (MCDs, CCDs, and other entities), American Indian and Alaska Native areas (AIANAs), census tracts and block numbering areas (BNAs), and block groups. A UA boundary cannot subdivide a tabulation census block.

There are significant regional variations in the shape and growth patterns of UAs. These differences stem from many factors. Often they relate to the dominant settlement patterns within particular areas, or to topography, environmental factors, and historical circumstances. For instance, the various State and local statutes governing the incorporation of places can influence the shape of UAs. Also, different land survey systems affect the location of property lines, the location of streets and roads, the layout of census blocks, and, ultimately, the shape of the UA and the location of its boundaries. Steep slopes and the presence of large water boundaries can constitute physical barriers to development, and often affect population densities, the layout of census blocks, and the location of some segments of the UA boundary. By contrast, UAs surrounded by abundant developable land may be more susceptible to urban sprawl. These are only some of the regional differences that shape UAs and present challenges to delineating them consistently on the basis of a single set of national criteria.

The Census Bureau releases several series of printed reports that are grouped under three broad titles: 1990 Census of Population and Housing (CPH), 1990 Census of Population (CP), and 1990 Census of Housing (CH). Notes and References 12-18Urban and Rural Classifications