This directory contains the 1:100,000-scale Land Use and Land Cover (LULC)
Data.

*** If you have any questions or suggestions, please contact Customer  ****
    Services at custserv@edcserver1.cr.usgs.gov
    
DIRECTORY STRUCTURE
The directory structure for the 1:100,000-scale LULC FTP account
is defined as follows:
     A-Z/mapname
     where:
          A-Z = The first letter of the 1:100,000-scale map name.
     mapname  = The name of the 1:100,000-scale map.

The data files, which are located under the map name subdirectory, 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.  If you
do not have access to gzip, the FTP server will uncompress the file
as you retrieve it.  To do this, simply leave off the ".gz" extension 
when retrieving the file (NOTE: This option is not available through MOSAIC).  
For example, to retrieve the file "census.gz" without compression just use 
"get census".  Note that the uncompressed files are typically five times 
larger than the compressed versions and will take five times longer to 
transmit.  The gzip program is available via anonymous FTP at the
following sites:
     prep.ai.mit.edu:/pub/gnu
     wuarchive.wustl.edu:/systems/gnu

The data files are stored on a robotic mass-storage device so there
may be a short (~10 seconds) delay while the media is retrieved.

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 located in the FTP account do NOT contain record 
delimiters.  Once you down load the files, 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. 

***
For a complete explanation of the 1:100,000-scale LULC data see the USGS 
National Mapping Program, Technical Instructions, Data Users Guide 4, "Land
Use and Land Cover Digital Data from 1:250,000- and 1:100,000-scale Maps".
This booklet can be ordered, for a small fee, from the Earth Science 
Information Center at the following address:

Earth Science Information Center
U.S. Geological Survey
507 National Center
Reston, VA  22092
Tel:  783-648-6045 or 800-USA-MAPS
Fax:  783-648-5548
 
Information about the LULC data set can also be found through the World Wide 
Webb (WWW) at the following URL address: 
http://edcwww.cr.usgs.gov/glis/hyper/guide/1_250_lulc 

The Global Land Information System (GLIS) also provides on-line data set
documentation.