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 the boundaries established for these entities, often including the names of the features that constitute the boundaries.

Boundaries, in particular, are an important element in communicating the exact location of a specific geographic entity to data users. State and local governments record the location of legal boundaries following the requirements of law. Such boundaries typically run through space or follow a major physical feature such as a river or ridge. The Census Bureau requires that the boundaries of statistical entities be easily recognizable linear features (roads, railroads, streams) that are identifiable through observation in the field. This requirement originally stemmed from the need for enumerators to know the exact limits of the areas they were assigned to canvass—a condition that still applied to many phases of the 1990 decennial census. The use of such definite, easily recognized boundaries also makes it possible for data users to relate information from local records or other sources to the appropriate statistical entity. To those data users not familiar with a particular area, the boundary information on Census Bureau maps depicts a definite, precise network of small geographic entities.

Size is an important consideration in creating statistical entities and in making widespread changes to an existing set of such entities. To many data users, size refers to the number of people, housing units, or economic establishments within an area rather than the geographic extent of the area. The Census Bureau provides population size guidelines in its criteria for most types of statistical entities; the size criterion generally determines the maximum number of such entities that someone can establish within a given county or other jurisdiction. The observation of minimum population size guidelines for statistical entities also helps to ensure confidentiality.

In the context of population size, the statistical reliability of the data presented for various geographic units also becomes a significant factor. Because many of the Census Bureau’s data tabulations involve the use of Geographic Overview2-31