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<br />Distribution Format <br /> <br />The optional distribution format was designed to facilitate data usage. The <br />topological relationships explicitly encoded include starting node, landing node, <br />area to the left of direction of travel, and area to the right of the direction <br />of travel for line elements, bounding lines for area elements, and bounded lines <br />for node elements. These files can simplify processing requirements. For <br />example, because topological linkages are explicitly encoded for all line, node, <br />and area elements, a polygon data structure can be easily created. These <br />linkages facilitate Geographic Information System (GIS) applications of DLG data <br />as well as generation of graphic products, <br /> <br />The files are physically comprised of ASCII characters organized in~o fixed- <br />length logical records of 80 characters (bytes). Bytes 1-72 of eaeh record <br />contain DLG data, and bytes 73-80 may be blank or contain a record sequence <br />number, <br /> <br />The record types used in the optional DLG distribution format may be categorized <br />as header and data records. <br /> <br />The actual sequence of records in an optional distribution format DLG file is as <br />follows: <br /> <br />1, Header record" <br />Ten fil" identification and <br />description records <br />Control point identification records <br />(one per control point) <br />Data category identification records <br />(one per data category in the file) <br /> <br />2, <br /> <br />Data records <br />Node id"ntification record <br />Node to-line linkage record(s) <br />Attribute Code record(s) <br /> <br />Repeated <br />for each <br />node within a <br />data category <br /> <br />Area identification record <br />Area-to-line linkage record(s) <br />Attribut:e code record(s) <br /> <br />Repeated <br />for each <br />area wi thin a <br />data category <br /> <br />Line identification record <br />Coordim,te string record(s) <br />Attribut:e code record(s) <br /> <br />Repeated <br />for each <br />line within a <br />data category <br /> <br />Descriptions of the contents of the various types of records in an optional <br />format DLG follow, <br /> <br />10/93 <br /> <br />6 <br />