Page:Geographic Areas Reference Manual (GARM).pdf/189

 The place on which a CCD is centered usually is an incorporated place or a census designated place (CDP). Ideally, it should never subdivide such entities; when it must, as much of the place as possible should be one CCD. In some cases, the CCD is centered on a major area of significantly different land use or ownership, such as a large military base or American Indian reservation; in other situations, it can represent an area that is physiographically different from the rest of the county. A CCD should always consist of a single geographic piece that is relatively compact in shape.

The criteria for CCD boundary features are the same as those for census blocks, census tracts, and BNAs (for details, see, “Census Tracts and Block Numbering Areas” and , “Census Blocks and Block Groups”). A CCD should have easily locatable boundaries that seldom change. They should be readily discernable in the field and easy to depict on the Census Bureau’s maps. They should follow physical features, such as highways, roads, railroads, rivers, streams, power transmission lines, trails, or mountain ridges. A few kinds of non-physical features are used; for example, county lines always are CCD boundaries. In certain situations it is permissible to use point-to-point lines (comparatively short projected lines between two definite points); also permissible are conjoint city limits (a common boundary between two contiguous incorporated places). As a result of these guidelines, the CCD boundaries identify a stable set of geographic entities that allows the data user to make historical comparisons at the county subdivision level.

The geographic area of a CCD, or the community or place on which it is centered, almost always fits within the existing census tracts or BNAs. A CCD usually consists of one or a combination of contiguous census tracts or BNAs. It seldom subdivides a census tract or BNA. The result is a geographic pattern of county subdivisions wherein the data user can relate the CCDs to their smaller geographic components. 8-18County Subdivisions