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<br />degenerate line starts and ends at the same node, has two identical coordinate <br />pairs, has zero length, and has the same area to the left and right of the <br />direction of trave l; that is, it is totally enclosed inside one map area. <br />Topologically, a dEgenerate line is considered to be a fully connected line, <br />since the attached node has a node-line list count of two. <br /> <br />An area is a continuous, unbroken region of the map bounded by lines. Each area <br />is identified in a DLG-3 data file by a unique area point located inside the area <br />it represents. Also, every DLG data file will have at least two areas <br />identified: one representing the area covered by the file and the other <br />representing the area outside the coverage of the file. Polygons as unique <br />features are not defined explicitly in a DLG file. However, polygons can be <br />constructed using lene-area linkages built into the DLG data structure, <br /> <br />Attribute Codes <br /> <br />In addition to locational and topological information, DLG data elements have <br />explicitly encoded .3ttributes. Attribute codes, also called feature codes or <br />classification attributes, are used to describe the map information represerted <br />by a node, area, or line, For example, the attribute code for an area might <br />identify a lake or swamp; the attribute code for a line might identify a stream, <br />or shoreline. A lis ting of all the attribute codes currently assignee, and used <br />in FEMA DLG files is contained in this document. <br /> <br />Each attribute codE~ identifies the major category to which a cLata elenent <br />belongs, as well as the specific nature of the element. Codes also may provide <br />additional descriptive information. Most elements are uniquely described by a <br />single attribute code. Others, however, may require two or more codes for a <br />complete description. If multiple attributes are needed to describe an element, <br />the order is significant. Allowing for a variable number of attrib~te codes <br />creates an open-ended structure to which information may be added .3t any time. <br /> <br />A DLG attribute code is composed of two distinct numeric fields: a three~digit <br />maj or code, which id,mtifies the maj or category to which the element belongs, and <br />a four-digit minor code, which specifically describes the element. In the <br />digital file, the major and minor attributes are encoded in two in'teger fields <br />of six digits, right justified with leading blanks (FORTRAN 216 format), In this <br />docwnent, maj or codes are presented as three digi ts, and minor codes are <br />presented as four digits. Leading zeros are shown for clarity; for example: 440 <br />0245. <br /> <br />MaioI' Attribute COdES <br /> <br />The first two digits of the major code uniquely identify the category to which <br />the described element belongs. The third digit of the major code i:; used to <br />modify the minor coe,e in two ways: <br /> <br />. <br /> <br />If zero, the minor code represents a description or classification <br />of the element. <br /> <br />10/93 <br /> <br />4 <br />