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<br />tr <br />l <br /> <br />- <br /> <br />GENERAL <br /> <br />The Federal Emergency Management Agency (FEMA) is collecting and distributing <br />digital thematic data pertaining to flood hazard identification and flood <br />insurance. The standards specified in this document pertain to the collection, <br />processing and revision of Digital Line Graph (DLG) data intended for <br />distribution by FEMA. <br /> <br />These standards are intended to facilitate the interchange and use of DLG data. <br />DLG collection and processing systems must produce data that are compatible with <br />other production systems not only within the Federal sector but also within other <br />government and private sector organizations. Due to rapidly changing <br />technologies in the mapping industries, these DLG standards cover a broad range <br />of collection and processing systems. It is not the intent of this standard to <br />inhibit usage of any procedure, but to set common standards which will allow data <br />to be acceptable for entry into many different production systems. The basic <br />applications of DLG dat~ are to suppcrt automation of cartographic processes a~~ <br />automated spatial data analysis. <br /> <br />The DLG file structure is designed to accommodate all categories of spatial data <br />represented on a conventional map. Node, line, and area data types are accepted. <br />Th~ attribute coding scheme is designed to accommodate basic thematic data <br />categories such as political, map panel, hydrographic, and flood hazard zone <br />features. <br /> <br />Data Sources <br /> <br />Digital Line Graph data are usually derived by digitizing map features as line <br />graph elements from cartographic source materials. The map name, community name, <br />scale, date, and projection of the source materials is contained in the Metadata <br />file. ' <br /> <br />Data Content <br /> <br />The DLG files derived from the Flood Insurance Rate Maps (FIRMs) contain selected <br />categories of thematic data in digital form; these data categories do not <br />necessarily correspond to the traditional feature separates associated with the <br />maps. <br /> <br />The following categories are valid for DLG files published by FEMA: <br /> <br />. Political Areas This category of data consists of political <br />subdivisions, e.g. city, county, state. <br /> <br />. <br /> <br />Hap Panel Areas - This category of data consists of FEMA' 5 map <br />panelling schema. <br /> <br />. <br /> <br />FEMA Hydrography - This category of data consists of <br />water control structures and surface water. <br /> <br />10/93 <br /> <br />1 <br />