DATABASE NAME

     COUNTY:  1:100,000 base map scale County Boundaries
     Integrated with Shorelines

DATABASE DESCRIPTION

     1:100,000 base map scale county boundaries integrated with
     shorelines for the United States.

ORIGINATING AGENCY

     Federal Highway Administration, Office of Environment and
     Planning

AGENCY RESPONSIBLE FOR MAINTAINING DATA

     Federal Highway Administration, Office of Environment and
     Planning

CONTACT

     National Transportation Atlas Databases
     Bureau of Transportation Statistics
     U.S. Department of Transportation
     Washington, DC  20590
     (202) 366-DATA
     Internet:  info@bts.gov

SOURCE

     1990 1:100,000 Census TIGER/Line records integrated with the
     1:250,000 NOAA shorelines supplemented by editing performed
     by the University of Tennessee for the Federal Highway
     Administration

ACCURACY

     80 m (165 mi) root-mean square positional accuracy of
     political boundaries

TYPE OF GIS DATABASE

     Area database with polygons and links

FILES/SIZE/NUMBER OF RECORDS

     Two ASCII files

     1)   county.ply     polygon file contains area attributes
     2)   county.lin     link file contains link attributes,
                         locations, and shapes

     Approximate size of files:    56,823,000 bytes
     Approximate number of areas:  15,700
     Approximate number of links:  

FILE STRUCTURE

     The files are fixed format.

     The Polygon File

     The Polygon Record File contains a single 92 byte record for
     each polygon representing a large urban area, delimited by a
     CR/LF.  Each Polygon Record contains the following
     structure.

          COLUMN         TYPE       WIDTH

          RECTYPE        char           1
          VERSION        short int      2
          RECID          long int       8
          SOURCE         char           1
          SQMILES        float          12
          SQKM           float          12
          STFIPS         short int      2
          CTFIPS         short int      5
          CTNAME         char           25
          CENTER_X       float          12
          CENTER_Y       float          12

     Each field in the Polygon File is described more fully
     below:

     RECTYPE
          Data Type:          Character
          Width:              1
          Starting Position:  1
          Domain:             'P'
          Description:        Identifies Polygon Records

     VERSION
          Data Type:          short int
          Width:              2
          Starting Position:  2
          Domain:             positive integers
          Description:        This field describes the release
                              version of the database.  The
                              VERSION code consists of a leading
                              Version Number and a trailing
                              Revision Number; thus, 10 denotes
                              Version 1 Revision 0.  Similarly, a
                              VERSION value of 21 would denote
                              Version 2 Revision 1.

     RECID
          Data Type:          long int
          Width:              8
          Starting Position:  4
          Domain:             positive integers
          Description:        The RECID is a unique numeric
                              identifier associated with each
                              Polygon Record.  RECIDs are
                              permanent and are not reused.

     SOURCE
          Data Type:          Character
          Width:              1
          Starting Position:  12
          Domain:             'U'
          Description:        The SOURCE flag is used to describe
                              the original source of the CTNAME
                              attribute data in the Polygon
                              Record.  
                                   'U'  University of Tennessee
                                        source
                              Other source flags may be included
                              in future releases of the database.

     SQMILES
          Data Type:          float
          Width:              12
          Decimal Places:     3
          Starting Position:  13
          Domain:             positive real numbers
          Description:        The SQMILES field is an
                              approximation of the area of the
                              polygon in square miles

     SQKM
          Data Type:          float
          Width:              12
          Decimal Places:     3
          Starting Position:  20
          Domain:             positive real numbers
          Description:        The SQKM field is an approximation
                              of the area of the polygon in
                              square kilometers

     STFIPS
          Data Type:          short int
          Width:              2
          Starting Position:  37
          Domain:             positive integers
          Description:        The FIPS code for the state within
                              which the polygon is contained.

     CTFIPS
          Data Type:          short int
          Width:              5
          Starting Position:  39
          Domain:             positive integers
          Description:        The FIPS code for the county within
                              which the polygon is contained.

     CTNAME
          Data Type:          Character string
          Width:              25
          Starting Position:  44
          Domain:             printable ASCII characters
          Description:        The CTNAME filed consists of a
                              descriptive name for the polygon
                              feature.  The description is left
                              justified in the field.  The CTNAME
                              field may contain embedded blanks.

     CENTER_X
          Data Type:          float
          Width:              12
          Decimal Places:     6
          Starting Position:  69
          Domain:             real numbers
          Description:        The longitude location in decimal
                              degrees for the calculated centroid
                              of the polygon.

     CENTER_Y
          Data Type:          float
          Width:              12
          Decimal Places:     6
          Starting Position:  81
          Domain:             real numbers
          Description:        The latitude location in decimal
                              degrees for the calculated centroid
                              of the polygon.

     The Link File

     The Line Record File contains a single 41 byte header record
     for each line in the large urban database, followed by a
     list of shape points stored in multiple 96 byte records. 
     The maximum number of shape points for any line is set to
     500.  All records are delimited with a CR/LF.  Line Records
     are either boundaries or closure lines which are used to
     artificially delineate polygon boundaries when no physical
     boundary exists.  For example state borders are modeled as
     closure lines.  Each Line Record contains the following
     structure.

               COLUMN         TYPE       WIDTH

               RECTYPE        char           1
               VERSION        short int      2
               RECID          long int       8
               SOURCE         char           1
               STFIPSL        short int      2
               STFIPSR        short int      2
               CTFIPSL        short int      5
               CTFIPSR        short int      5
               NPOINTS        short int      3

     The line record is followed by NPOINTS coordinates tuples
     stored in FORTRAN(8F12.6) format.  Each tuple is stored as
     X,Y (longitude, latitude) in decimal degrees.  Each field in
     the Line File is described more fully below.

     RECTYPE
          Data Type:          Character
          Width:              1
          Starting Position:  1
          Domain:             'L'
          Description:        Identifies Line Records

     VERSION
          Data Type:          short int
          Width:              2
          Starting Position:  2
          Domain:             positive integers
          Description:        This field describes the release
                              version of the database.  The
                              VERSION code consists of a leading
                              Version Number and a trailing
                              Revision Number; thus, 10 denotes
                              Version 1 Revision 0.  Similarly, a
                              VERSION value of 21 would denote
                              Version 2 Revision 1.

     RECID
          Data Type:          long int
          Width:              8
          Starting Position:  4
          Domain:             positive integers
          Description:        The RECID is a unique numeric
                              identifier associated with each
                              Polygon Record.  RECIDs are
                              permanent are not reused.

     SOURCE
          Data Type:          Character
          Width:              1
          Starting Position:  12
          Domain:             'N', 'T'
          Description:        The SOURCE flag is used to describe
                              the original source of the
                              topographic data in the Line
                              Record.  The following flags will
                              be present:
                                   'N'  National Oceanic and
                                        Atmospheric
                                        Administration (NOAA)
                                        (1:250,000)
                                   'T'  Census TIGER/Line Records
                                        (1:100,000)
     
     STFIPSL
          Data Type:          short int
          Width:              2
          Starting Position:  13
          Domain:             positive integers
          Description:        The FIPS code for the state to the
                              left of this line.

     STFIPSR
          Data Type:          short int
          Width:              2
          Starting Position:  15
          Domain:             positive integers
          Description:        The FIPS code for the state to the
                              right of this line.
     CTFIPSL
          Data Type:          short int
          Width:              5
          Starting Position:  17
          Domain:             positive integers
          Description:        The FIPS code for the county to the
                              left of this line.
     CTFIPSR
          Data Type:          short int
          Width:              5
          Starting Position:  22
          Domain:             positive integers
          Description:        The FIPS code for the county to the
                              right of this line.

     NPOINTS
          Data Type:          short int
          Width:              3
          Starting Position:  27
          Domain:             positive integers
          Description:        The number of shape points to
                              follow in the Line Record.


DISCUSSION

     Introduction

     This document describes the format and structure of the
     County Borders geographic database.  The County Borders
     database is a geographic database consisting of political
     boundaries or coastlines/shorelines for the United States
     and selected territories.  This database was compiled by
     members of the Geographic Information Systems Group at the
     University of Tennessee, Pellissippi Research Institute in
     Knoxville, Tennessee for the Federal Highway Administration,
     Office of Environment and Planning, HEP-11.  It was
     developed as a mapping database for use within Geographic
     Information Systems and other computer-aided mapping
     software.

     Overview

     The County Borders database contains polygon and line
     records for the 48 contiguous states, Washington DC, Alaska,
     Hawaii, and Puerto Rico.  It is distributed in two files: a
     Polygon Record File and a Line Record File.  Each file
     contains fixed length ASCII records and is organized such
     that each state will build as a complete set of polygons. 
     Closure is achieved by adding lines (closure lines) to
     artificially bound polygons where no physical boundary
     exists such as at a state boundary where an urban area
     straddles more that one state.  The database is constructed
     using a DIME-like file structure.  The DIME structure
     encodes polygon topology onto line segments by defining left
     and right side polygon attributes and attributing each line
     in the database with unique direction.  The DIME structure
     enables polygons sharing common boundaries to be modeled
     simply, without redundant lines being present in the
     database.  Associated with each polygon is a centroid which
     references a polygons attribute information.  A single
     infinitely large unbounded polygon, termed the external or
     universal polygon, is defined to ensure complete closure of
     all polygons in the database.  Every polygon in the database
     lies within the universe polygon.

     Each feature in the database has a unique permanent record
     identifier, and each record contains a descriptive section
     which references the version and source of the original
     data.  The external polygon is always reference with a
     polygon ID of 0(zero).  Note that the universe polygon has
     no polygon record or centroid associated with it.

     Data Sources

     The County Borders database was compiled from two sources. 
     CENSUS TIGER/Line files were sued for political boundaries
     in the contiguous 48 states, as well as national and coastal
     boundaries in Alaska, Hawaii, and Puerto Rico.  Digital data
     from the National Oceanic and Atmospheric Administration
     (NOAA) were used to represent coastal boundaries and
     shorelines in the contiguous 48 states.

     Area attributes for the polygons were calculated using
     Arc/Info V6.1.1 GIS Software (ESRI 1991).  Other map
     features and attributes such as closure lines and FIPS codes
     were added by members of the development staff.
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