"The characteristics of the digital cartographic data base for land Use and land cover and associated maps reflect the parameters used in compiling the maps. The Land Use and Land Cover mapping program is designed so that standard topographic maps at a scale of l:250,000 can be used as a base for compilation and reproduction. In a few cases, the U.S. Geological Survey (USGS) has prepared Land Use and Land Cover and associated maps at a scale of 1:100,000 when the 1:100,000-scale topographic map base was available... Land Use and Land Cover maps provide data to be used either by themselves or in combination with the other data sets produced in the program. The basic sources of land use compilation data are NASA high-altitude aerial photographs, and National High-Altitude Photography (NHAP) program photographs, usually at scales smaller than l:60,000. The l:250,000-scale topographic map series is generally used as the base map for the compilation of the Land Use and Land Cover maps and the associated overlays; 1:100,000-scale topographic map bases have been used on rare occasions. Although compilation of Land Use and Land Cover data is performed on a film-positive base usually enlarged to a scale of approximately l:l25,000, the associated overlays are both compiled and digitized at a scale of l:250,000. Land Use and Land Cover data compilation is based upon the classification system and definitions of Level II Land Use and Land Cover [codes, (see below)]... All features are delineated by curved or straight lines that depict the actual boundaries of the areas (polygons) being described. The minimum size of polygons depicting all Urban or Built-up Land (categories 11-17), Water (51-54), Confined Feeding Operations (23), Other Agricultural Land (24), Strip Mines, Quarries, and Gravel Pits (75) and urban Transitional areas (76), is 4 hectares (ha). All other categories of Land Use and Land Cover have a minimum polygon size of 16 ha. (Those sizes also are considered the minimum sizes to which polygons are digitized.) In the Urban or Built-up Land and Water categories, the minimum width of a feature to be shown is 200 m; (that is, if a square with sides 200 m in length is delineated, the area will be 4 ha). Although the minimum-width consideration precludes the delineation of very narrow and very long 4-ha polygons, triangles or other polygons are acceptable if the base of the triangle or minimum width of the polygon is 200 m in length and if the area of the polygon is 4 ha. Exceptions to this specification are limited access highways (14) and all double line rivers (51) on the 1:250,000-scale base which shall have a minimum width of 92 m. For categories other than Urban or Built-up Land and Water, the 16-ha minimum size for delineation requires a minimum-width polygon of 400 m. Line weight for delineating Land Use and Land Cover polygons and for neatlines is 0.l0 mm at the production scale of l:250,000."--- end quote
1 Urban or built-up land 11 Residental 12 Commercial and services 13 Industrial 14 Transportation, communication, utilities 15 Industrial and commercial complexes 16 Mixed urban or built-up land 17 Other urban or built-up land 2 Agricultural land 21 Cropland and pasture 22 Orchards, groves, vineyards, nurseries, and ornamental horticultural 23 Confined feeding operations 24 Other agricultural land 3 Rangeland 31 Herbaceous rangeland 32 Shrub and brush rangeland 33 Mixed rangeland 4 Forest land 41 Deciduous forest land 42 Evergreen forest land 43 Mixed forest land 5 Water 51 Streams and canals 52 Lakes 53 Reservoirs 54 Bays and estuaries 6 Wetland 61 Forested wetland 62 Nonforested wetland 7 Barren land 71 Dry salt flats 72 Beaches 73 Sandy areas not beaches 74 Bare exposed rock 75 Strip mines, quarries, gravel pits 76 Transitional areas 77 Mixed Barren Land 8 Tundra 81 Shrub and brush tundra 82 Herbaceous tundra 83 Bare ground 84 Wet tundra 85 Mixed tundra 9 Perennial snow or ice 91 Perennial snowfields 92 GlaciersPROCESSING DETAILS
-- Converts the USGS data files to polygon coverage format. -- Reconstructs topology, creating line and polygon features. -- Linearly scales the map coordinates to UTM using the registration points listed in the USGS data file, and then modifies the coordinates to Albers Equal Area projection. -- Generates a quadrangle boundary polygon based on the mathematically-determined corners of the map. -- Loads available documentation into a series of companion documentation files with each data set.Another AML program (GIRASNEAT, <http://www.epa.gov/ngispgm3/spdata/EPAGIRAS/meta/girasneat.aml>) does the following:
--clips the data to the neatline data set. --dissolves polygon boundaries between polygons with the same land use code. --snaps exterior arcs to the arcs of the neatline cover with a tolerance of 40 meters.Data were reviewed visually by the user responsible for executing the GIRASARC2 program.
filename.shp ESRI shapefile geographic data file filename.shx ESRI shapefile index data file filename.dbf ESRI shapefile attribute file filename.prj "Well-Known-Text" (WTK) format projection file filename.shp..xml metadata fileThe shapefiles use geographic (decimal degree) coordinate data referenced to the North American Datum of 1983.
IMAGE XMIN YMIN XMAX YMAX DESCRIPTION giras1 -2380005 1874985 15 3200000 NW Conterminous US (Albers) giras2 15 1874985 2300000 3172005 NE Conterminous US (Albers) giras3 -2380005 199995 15 1874985 SW Conterminous US (Albers) giras4 15 199995 2300000 1874985 SE Conterminous US (Albers) giras5 369285 2081265 955575 2460585 Hawaii (UTM Zone 4) giras6 499875 6762705 662145 6877755 Valdez, Alaska (UTM Zone 6)The raster data sets are referenced to locations specified in projected coordinates (in meters). Image tiles giras1 through giras4 use standard parameters for the conterminous United States:
Projection ALBERS Datum NAD83 Units METERS Spheroid GRS1980 Xshift 0.0000000000 Yshift 0.0000000000 Parameters 29 30 0.000 /* 1st standard parallel 45 30 0.000 /* 2nd standard parallel -96 0 0.000 /* central meridian 23 0 0.000 /* latitude of projection's origin 0.00000 /* false easting (meters) 0.00000 /* false northing (meters)giras5 (Hawaii) uses these projection parameters:
Projection UTM Zone 6 Datum NAD83 Units METERS Spheroid GRS1980giras6 (Valdez, Alaska) uses these projection parameters:
Projection UTM Zone 4 Datum NAD83 Units METERS Spheroid GRS1980The raster data sets are distributed as a collection of related files:
girasX.tif Tagged-Image Format File (TIFF) with GeoTIFF georeferencing girasX.tfw ESRI "World file", used for georeferencing girasX.aux ESRI "aux file" file used by ArcGIS software girasX.prj ESRI ArcInfo projection file girasX.tif.xml metadata fileUSGS DISCLAIMERS: