USGS:
This data set is released as part of an enhanced version of previously published
USGS land-use and land-cover data, edited to perform attribute and geographic
corrections, recast to the North American Horizontal Datum of 1983, and
reformatted to the commonly used geospatial data file formats.
BACKGROUND
The following background information is extracted from:
U.S. Geological Survey, 1986, Land use and land cover digital data from
1:250,000- and 1:100,000-scale maps: Data User Guide 4, 25 p.
(This document is out of print, but was available online on July 1, 2005 at
<http://www.vterrain.org/Culture/LULC/Data_Users_Guide_4.html>)
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"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."
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LAND-USE AND LAND-COVER CODES
These data sets represent land use and land cover using an integer value that
references the Anderson level II classification system.
The first digit represents the level 1 land-use and land-cover code, and the second
digit (ones place) represents a subdivision, or level 2 code.
The Anderson Level II land use codes used in this data set are listed below:
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 Glaciers
PROCESSING DETAILS
The U.S. Environmental Protection Agency (USEPA) received the USGS land-use and
and land-cover data files from USGS in 9-track ASCII format, one file per quadrangle.
Files were loaded onto the hard disk of the computer from tape. The data were then
processed with the GIRASARC2 program written in Arc Macro Language (AML), which
is part of the ArcInfo Geographic Information System (GIS) software. This program was
developed by the USGS to process the data into a consistent ArcInfo format.
The GIRASARC2 AML
<http://www.epa.gov/ngispgm3/spdata/EPAGIRAS/meta/girasarc2.aml>
program does the following:
-- 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.
The GIRASARC2 and GIRASNEAT programs were executed in AML to create each quadrangle data set.
The processing described above was completed by the USEPA in the early 1990s. In 2001,
the USGS National Water-Quality Assessment (NAWQA) Program needed a seamless data
base of the conterminous United States, so data sets were further enhanced for use in the
Program, as described below.
Additional land use and land cover data sets for Hawaii and one map sheet in Alaska were
converted using the same AML programs and edited in a similar manner. The Hawaii data
sets were joined together into a single data set as they all are documented with the same
source date and are more easily handled as a single data file.
These data files were then further edited to correct land-use coding errors caused by the
misplacement of labels have also been corrected by visual inspection, checking the codes
against the original labels in the GIRAS data files and ancillary land-cover data sets. An AML
menu-based application was used to assist in this process.
In addition to the processing describe above, the data were processed to fill in all gaps between
quadrangles so that the data fits together seamlessly. The polygon data were then transformed
so that the horizontal coordinate data reference the North American Datum of 1983. (The raw
GIRAS-format data and the USEPA version of it is referenced to the North American Datum of
1927.) The geographic data files were also projected into geographic coordinates (decimal
degrees of latitude and longitude). Additional polygon data sets that document the land-use
and land-cover data sets in a geographic context were created from the USEPA quadrangle
index coverages with further editing based on information in the USGS data files posted on the
USGS FTP site at the USGS EROS Data Center at: <ftp://edcftp.cr.usgs.gov/pub/data/LULC>
A summary of this effort was published as: Price, C., Naomi, N., Hitt, K., and Clawges, R., 2003,
Mining GIRAS: Improving on a national treasure of land use data, _in_ Proceedings of the 2004
ESRI International User Conference, July 7-11, 2003, Environmental Systems Research Institute,
Redlands Calif., 11p., available online at <http://gis.esri.com/library/userconf/proc03/p0904.pdf>
DATA FILE DESCRIPTIONS
Note that all data sets are referenced to the North American Datum of 1983.
1. tilepoly: Polygons representing each quadrangle tile.
2. src_poly: Polygons representing the extent of source files, with metadata about the source files
used for each area. Some land-use files were merged from multiple GIRAS source files, some of
which have different source dates.
3. gAABBB: Polygons for each 1:250,000 tile, where "AA" represents the latitude of the lower right
corner and "BBB" represents the longitude of the lower right corner of the map tile.
These tile names are referenced in the polygon attributes of the tilepoly and src_poly polygon data
sets described above.
The polygon data sets above are distributed as a collection of related files that make up the publicly
documented ESRI shapefile format:
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 file
The shapefiles use geographic (decimal degree) coordinate data referenced to the
North American Datum of 1983.
4. girasX Raster-format data, stored in six image files,
in GeoTIFF format (with georeferencing included in the
internal image header file).
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 GRS1980
giras6 (Valdez, Alaska) uses these projection parameters:
Projection UTM
Zone 4
Datum NAD83
Units METERS
Spheroid GRS1980
The 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 file
USGS DISCLAIMERS:
The use of trade, product, or firm names is for descriptive purposes only and does not imply
endorsement by the U.S. Government.
Although this Federal Geographic Data Committee-compliant metadata file is intended to document
the data set in nonproprietary form, as well as in ArcInfo format, this metadata file may include some
ArcInfo-specific terminology.
Although these data have been used by the U.S. Geological Survey, U.S. Department of the Interior,
no warranty expressed or implied is made by the U.S. Geological Survey as to the accuracy of the data.