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 mile (in the case of jumps, 500 or more), and the territory can be added to the UA.

As with jumps and nonresidential urban land uses, undevelopable territory also is used in some cases to link an outlying cluster of densely settled territory to the main body of the UA. The Census Bureau designates territory as undevelopable only if it consists of water area, mud flats, swamps, marshlands, steep slopes, and other terrain where development is nonexistent and new development is virtually impossible because of the physical limitations; such territory must not contain any existing housing or commercial structures. There must be a road connection from the main body of the UA through the undevelopable territory to the outlying densely settled area, and the road distance cannot exceed five miles.

Indentations occur where a low-density census block or cluster of blocks protrudes into the main body of the UA. Indentations almost always consist of territory outside of any place (only very rarely are they small incorporated places or CDPs). Indentations formed by the boundaries of incorporated places usually occur more frequently than those involving only territory outside of any place. The inclusion of indentations smooths the UA boundary, gives it a more regular appearance, and simplifies its presentation on maps.

The Census Bureau includes an indentation in the UA if it is: All of the above conditions must apply. Notes and References Urban and Rural Classifications12-9
 * Flanked by territory that has an average density of at least 1,000 inhabitants per square mile.
 * Less than one mile wide across its open end.
 * At least two times deeper than it is wide.
 * Five square miles or less in size.
 * Closeable by means of a block boundary located across or close to its open end.