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1:100,000-scale Land Use and Land Cover (LULC)
The data files adhere to the follow naming convention: land_use = Land Use and Land Cover (GIRAS format) political = Political Units (GIRAS format) hydro = Hydrologic Units (GIRAS format) census = Census County Subdivision (GIRAS format) federal = Federal Land (GIRAS format) state = State Land (GIRAS format) grid_cell = Composite Theme Grid format (all layers) FILE COMPRESSION The files have been compressed with the GNU "gzip" utility. DATA CONTENT: The set of Land Use and Land cover and associated maps consists of Land Cover, political units, hydrologic units, census county subdivisions, Federal land ownership, and State land ownership. The Land Use and Land Cover map is compiled to portray the Level II categories of the Land Use and Land Cover classification system documented by Anderson and others (1976). The Level II categories of this Land Use and Land Cover classification system provide the user with a basic framework to which third- and fourth-level categories may be added. The associated maps portray either natural or administrative information. They provide the user with the opportunity to utilize the Land Use and Lanar Cover maps and data, either individually or collectively, to produce graphic or tabular data for the areas portrayed on the associated maps. This mapping system is constructed in such a way that the Land Use and Land Cover data can be related to other resource fields such as soils, geology, hydrology, and demography. DATA FORMAT The LULC data are available in two formats: GIRAS and CTG. GIRAS Format: The geographic information retrieval and analysis system (GIRAS) format involves a standard character fixed length record (usually ASCII-coded, 80-character logical record). Each record may consist of 1 to 16 data- element fields, and each data element may be one of three different types: 1) 16-bit binary integer: 2) 32-bit binary integer or 3) a string of text characters. The GIRAS file structure is comprised of a map header, section header, arc records subfile, coordinate subfile, polygon records subfile, file of arcs by polygon (FAP) subfile, text subfile, and an associated data subfile. The LULC GIRAS files do NOT contain record delimiters. You can add delimiters using the following UNIX command: dd if=inputfilename of=outputfilename ibs=8000 cbs=80 conv=unblock CTG Format: The Composite Theme Grid (CTG) format involves representing data in raster or grid cell form for a given quadrangle. The CTG files are sequential and consist of fixed length records (except for header files) with one grid cell for each logical record. The grid cells are actually a regular point sample of the quad where the center point of each cell is 200 meters apart from other center points in adjacent cells. The cells are mapped to the UTM projection and oriented in the north-south, east-west directions. |
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