Page:Geographic Areas Reference Manual (GARM).pdf/279

 In instances where special area boundaries subdivide a census tabulation block, the Census Bureau allocates the data according to procedures agreed upon with the purchaser. For instance, the allocation may be on the basis of the land area of the subdivided part(s) or may require a detailed examination of 1990 census records.

The core area of most urban agglomerations consists of a grid system of relatively small blocks, disrupted here and there by water features; topographic relief; special land uses such as parks, industrial areas, and commercial areas; transport features such as airports and railyards; and institutions such as hospitals, schools, and detention facilities. The surrounding older suburbs tend to repeat this pattern; however, development since the 1960s often involved larger residential blocks with curvilinear street patterns and cul-de-sacs. This new pattern of urban development reflects the application of urban planning concepts and a concern for residential amenities. The road patterns in rural areas follow both a branching and a grid pattern, depending on local factors as well as the rural settlement patterns in particular regions of the Nation. Rural patterns greatly reflect the topography and land survey system that was in place at the time of settlement.

Regional variations in census block patterns are related to the age of the settlement pattern and the relative density of the population. In the urban cores of most older cities, census blocks are small because development preceded the introduction of urban transportation technologies (such as interurban railways, streetcars, and the automobile) and the decentralization of industries and jobs. Surrounding these urban cores in the eastern and southern regions of the Nation, one typically finds dense, irregular street patterns and an extensive system of connecting roads due principally to the metes and bounds survey system.

The presence of coastal and inland water features often influence the settlement pattern. In areas influenced by French settlement, such as within the Census Blocks and Block Groups11-19