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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 travel; that is, it is totally enclosed inside one map area. <br />Topologically, a degenerate line is considered to be a fully connected lene. <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 bo'mded by lines. Each area <br />is identified in a OLG-3 data file by a unique area poitlt located inside the area <br />it represents. Also, every OLG 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 uneque <br />features are not defined explicitly in a OLG file. However, polygons can be <br />constructed using line-area linkages built into the DLG data structure. <br /> <br />Attribute Codes <br /> <br />In addition to locational and topological information, OLG. data elements have <br />explicit) y encro'ed attributes. Attribute codeF. also called feature codes or <br />classification attributes, are used to describe t.le map infolCmation represented <br />by a node t area t or line. For example t the attribu'te 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 listing of all the attribute codes currently assigned and used <br />in FEMA OLG files is contained in this document. <br /> <br />Each attribute code identifies the maj or category to which a data element <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 IOttributes are needed to describe an element, <br />the order is significant. Allowing for a variable number of attribute codes <br />creates an open-ended structure to which information may be added at any time. <br /> <br /> <br />A OLG attribute code is composed of two distinct numeric fields: a three-digit <br />major code, which identifies the major category to whi,:h 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 enc"ded in two integer fields <br />of six digits, right justified with leading blanks (FORTRAN 216 format). In this <br />document, 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 />Maior 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 is used to <br />modify the minor code 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 />