National Transportation Atlas Database
================================================================================

                    Data Dictionary and Database Formats
                    ------------------------------------

The Bureau of Transportation Statistics (BTS) has created a standard set of
file formats for geospatial databases included in the National
Transportation Atlas (NTA). These formats were developed to make it easier
to view and extract NTA data by establishing a common structure for each of
the three geospatial feature types depicted in the NTA: points, networks,
and areas. These formats are also being provided to GIS software vendors so
that they can develop translation software to import the databases directly
into their own internal formats. The BTS will distribute all of its
geospatial data using these formats as an interim standard until a formal
Transportation Network Profile (TNP) is adopted as part of the Spatial Data
Transfer Standard (SDTS).

The BTS geospatial file formats are based on a set of standard record types.
Six distinct record types are currently defined: Link, Node, Point, Area,
Geography, and Attribute. [footnote 1] Each of the three spatial feature
types included in the NTA consists of an interrelated combination of these
record types defining the geometry, topology, and attributes associated with
a specific transportation or background feature. Feature types and their
composite record types are described below:

     Transportation Networks are composed of four related record types:
     Link, Node, Geography, and Attribute. Examples of transportation
     networks are highways, railroads, and waterways.

     Transportation Point Facilities such as airports, water ports, and
     truck terminals require only two related record types: Point and
     Attribute.

     Areas are made up of three related record types: Area, Geography, and
     Attribute. Features such as Congressional Districts, States, and
     National Parks are examples of areas.

Figure 1 illustrates the relationships among the record types for each
feature:


                File Linkage Relationships in the Databases
           Contained in within the National Transportation Atlas

      Transportation Networks                          Areas
      -----------------------                          -----

   File      Linking                        File      Linking
             Fields                                   Fields           
 ----------------------                    ----------------------
|           | LINKID   |<-------          |           | AREAID   |<----
|           |----------|        |         | Area      |----------|     |
|           | ANODE    |<----   |         |           | FEATURID |<-   |
| Link      |----------|     |  |          ----------------------   |  |
|           | BNODE    |<----|  |                                   |  |
|           |----------|     |  |          ----------------------   |  |
|           | FEATURID |<-   |  |         | Attribute | FEATURID |<-   |
 ----------------------   |  |  |          ----------------------      |
                          |  |  |                                      |
 ----------------------   |  |  |          ----------------------      |
| Attribute | FEATURID |<-   |  |         |           | LINEID   |     |
 ----------------------      |  |         |           |----------|     |
                             |  |         | Geography | AREAIDL  |<----|
 ----------------------      |  |         |           |----------|     |
| Node      | NODEID   |<----   |         |           | AREAIDR  |<----
 ----------------------         |          ----------------------
                                |
 ----------------------         |           Transportation Point Features
| Geography | LINKID   |<-------            -----------------------------
 ----------------------                      
                                             File       Linking
                                                        Fields
                                           -----------------------
                                          | Point     | FEATURID  |<--
                                           -----------------------    |
                                                                      |
                                           -----------------------    |
                                          | Attribute | FEATURID  |<--
                                           -----------------------



Each geospatial database distributed by the BTS will consist of a set of
files sharing a common file name and file extensions identifying the
corresponding record type. File names will be consistent with DOS file
naming conventions (e.g., eight characters or less, no spaces, etc.). The
file extensions for each record type are given below:

     .lnk link record type

     .nod node record type

     .pnt point record type

     .are area record type

     .geo geography record type

     .t__ attribute record type [footnote 2]

Each record type employs a standard ASCII character set and fixed length
records with fixed length attribute fields. The first four fields are the
same for every record type. They include the record type identifier, version
number, revision number, and modification date as described below:

     1 RECTYPE

          The RECTYPE identifies the record type associated with the file,
          where:

               L Link
               N Node
               P Point
               A Area
               G Geography
               T Attribute

          This field will have the same value for each record in the file.

     2 VERSION

          The version number is a 2-digit number that will be incremented
          for all records in the database whenever a new release is
          distributed.

          The BTS plans to issue a new release of each NTA database on an
          annual basis, incorporating updates of attribute fields as well as
          all corrections and enhancements made to the geography and/or
          topology since the previous release.

          Between each version release, the BTS will post interim updates on
          its Internet site, incorporating corrections identified by users
          and enhancement work in progress. Interim updates will include
          both a transaction database, containing only those records which
          have been updated since the last major release, and a transaction
          log file, identifying what specific changes were made to each
          updated record.

     3 REVISION

          The revison number is a 2-digit number that will be incremented
          individually for each record whenever a change is made to one of
          its fields. Revision numbers are also included in the transaction
          log file so that database users can identify what specific change
          was made to the record. Revision numbers will not be reset with
          each new release

     4 MODDATE

          The modification date indicates when each record in the database
          was last changed. For release 0100 this field is blank. As changes
          are made to a record, the modification date is entered in the
          format 'mmddyyyy'.

Following these first four fields, each record type has its own
characteristic set of fields. These fields are described below:

LINK FILE

The link file contains basic information related to transportation network
links. Each record contains the four standard fields (defined above) plus
seven additional fields.

     1 RECTYPE

     2 VERSION

     3 REVISION

     4 MODDATE

     5 LINKID

          The LINKID is a unique sequential number assigned to each record
          in the link file. It is used internally by most GIS software to
          index records and to establish topological relationships between
          spatial objects. It is not permanent and may change between
          different versions of the file.

     6 FEATURID

          The FEATURID is a unique character string or numeric value
          associated with the spatial feature. The metadata associated with
          each network database describes the significance of and method for
          assigning this identifier.

          While not necessarily a permanent identifier, the FEATURID is more
          stable than the LINKID. Any changes made in the FEATURID will be
          recorded in a transaction file maintained by the BTS and
          distributed with each new version of the database.

     7 ANODE

          The ANODE identifies a record (NODEID) in the node file that
          corresponds to the starting position of the link. [footnote 3]

     8 BNODE

          The BNODE identifies a record (NODEID) in the node file that
          corresponds to the ending position of the link.

     9 DESCRIPT

          The DESCRIPT field can contain any character string describing the
          link, such as a river name, route id name, or number. These
          descriptions need not be unique for each record.

     10 STFIPS1

          The STFIPS1 field contains the FIPS code for the State in which
          the link is located. If the link borders two States, STFIPS1
          contains the lower numeric value FIPS code.

     11 STFIPS2

          The STFIPS2 field contains the higher numeric value FIPS code for
          a second State in those cases where the link borders two States.
          If the link is located completely within a State, this field
          contains 00. In no case should a link border three or more States
          because a node should exist at the point where the States
          intersect.

NODE FILE

The node file contains basic information related to transportation network
nodes. Each record contains the four standard fields (defined above) plus
six additional fields.

     1 RECTYPE

     2 VERSION

     3 REVISON

     4 MODDATE

     5 NODEID

          The NODEID is a unique sequential number assigned to each record
          in the node file. It is used internally by most GIS software to
          index records and to establish topological relationships between
          spatial objects. It is not permanent and may change between
          different versions of the file.

     6 FEATURID

          The FEATURID is a unique character string or numeric value
          associated with the spatial feature. The metadata associated with
          each network database describes the significance of and method for
          assigning this identifier.

          While not necessarily a permanent identifier, the FEATURID is more
          stable than the NODEID. Any changes made in the FEATURID will be
          recorded in a transaction file maintained by the BTS and
          distributed with each new version of the database.

     7 LONGITUD

          The longitude of the node expressed as a signed integer with six
          (6) implied decimal places.

     8 LATITUDE

          The latitude of the node expressed as a signed integer with six
          (6) implied decimal places.

     9 DESCRIPT

          The DESCRIPT field can contain any character string describing the
          node, such as a town name, landmark, or border crossing point.
          These descriptions need not be unique for each record.

     10 STFIPS

          This field contains the FIPS code for the State in which the node
          feature is located. If the node is located on the border of two or
          more States, this field contains 00. If the node is located
          outside the borders of the United States, the field contains 99.

POINT FILE

The point file contains basic information related to transportation point
features and is similar to the network node file. Each record contains the
four standard fields (defined above) plus six additional fields.

     1 RECTYPE

     2 VERSION

     3 REVISION

     4 MODDATE

     5 POINTID

          The POINTID is a unique sequential number assigned to each record
          in the point feature file. It is used internally by most GIS
          software to index records. It is not permanent and may change
          between different versions of the file.

     6 FEATURID

          The FEATURID is a unique character string or numeric value
          associated with the point feature. The metadata associated with
          each point database describes the significance of and method for
          assigning this identifier.

          While not necessarily a permanent identifier, the FEATURID is more
          stable than the POINTID. Any changes made in the FEATURID will be
          recorded in a transaction file maintained by the BTS and
          distributed with each new version of the database.

     7 LONGITUD

          The longitude of the point feature expressed as a signed integer
          with six (6) implied decimal places.

     8 LATITUDE

          The latitude of the point feature expressed as a signed integer
          with six (6) implied decimal places.

     9 DESCRIPT

          The DESCRIPT field can contain any character string describing the
          point feature, such as a town name or airport. These descriptions
          need not be unique for each record.

     10 STFIPS

          This field contains the FIPS code for the State in which the point
          feature is located. If the point feature is located on the border
          of two or more States, this field contains 00. If the point
          feature is located outside the borders of the United States, the
          field contains 99.

AREA FILE

The area file contains basic information related to areal features. Each
record contains the four standard fields (defined above) plus six additional
fields.

     1 RECTYPE

     2 VERSION

     3 REVISION

     4 MODDATE

     5 POLYID

          The POLYID is a unique sequential number assigned to each record
          in the area file. It is used internally by most GIS software to
          index records and to establish topological relationships between
          spatial objects. It is not permanent and may change between
          different versions of the file.

     6 FEATURID

          The FEATURID is a unique character string or numeric value
          associated with the area feature. Where an area feature crosses a
          State boundary, separate records exist for the portions of the
          feature located within each State. For example, Yellowstone
          National Park exists as three records, one each for Wyoming,
          Montana, and Idaho. Each of those three records will have a unique
          POLYID but the same FEATURID. The metadata associated with each
          area database describes the significance of and method for
          assigning this identifier.

          While not necessarily a permanent identifier, the FEATURID is more
          stable than the POLYID. Any changes made in the FEATURID will be
          recorded in a transaction file maintained by the BTS and
          distributed with each new version of the database.

     7 CNTRLONG

          The longitude of the area feature record centroid expressed as a
          signed integer with six (6) implied decimal places. [footnote 4]

     8 CNTRLAT

          The latitude of the area feature record centroid expressed as a
          signed integer with six (6) implied decimal places.

     9 DESCRIPT

          The DESCRIPT field can contain any character string describing the
          area feature, such as a national park or military installation
          name. These descriptions need not be unique for each record.

     10 STFIPS

          The STFIPS field contains the FIPS code for the State in which the
          area feature is located. For those features which cross State
          boundaries, this field contains the FIPS code for the State in
          which the individual polygon is located.

GEOGRAPHY FILE

The geography file contains the shape information for network links or area
boundaries. The file structure includes a header record followed by a
variable number of shape point records. The header record contains the four
standard fields (defined above) plus four additional fields.

     1 RECTYPE

     2 VERSION

     3 REVISION

     4 MODDATE

     5 LINEID (LINKID)

          The LINEID is a unique sequential number assigned to each record
          in the geography file. It is used internally by most GIS software
          to index records and to establish topological relationships
          between spatial objects. In transportation networks the field name
          is LINKID, and matches the LINKID field in the Link File. It is
          not permanent and may change between different versions of the
          file.

     6 POLYIDL

          The polygon identification number (POLYID) from the area file for
          the polygon record located on the left side of the line. For
          transportation networks, this field is blank.

     7 POLYIDR

          The polygon identification number (POLYID) from the area file for
          the polygon record located on the right side of the line. For
          transportation networks, this field is blank.

     8 NPOINT

          The number of coordinate pairs (longitude and latitude) that
          define the shape of the linear feature and follow the header
          record. For transportation networks, the geography file includes
          the coordinates of both the start and end nodes of the link as
          well as all intermediate shape points. Therefore every linear
          feature will have at least two coordinate pairs.

ATTRIBUTE FILE

The attribute file(s) contains additional information about network links or
nodes, or point or area features. There may be multiple attribute files
associated with any geospatial feature database, and each attribute file may
have a different number of attributes and different attribute formats.
However, each specific attribute file is characterized by a fixed format and
fixed record lengths.

Each record in an attribute file contains the four standard fields (defined
above), one feature identification field, and a variable number of attribute
fields.

     1 RECTYPE

     2 VERSION

     3 REVISION

     4 MODDATE

     5 FEATURID

          The FEATURID is a unique character string or numeric value
          associated with the geospatial feature, and matches the FEATURID
          field in the corresponding Link, Node, Point, or Area files. This
          field provides the relational link between the spatial object
          which is used to represent a feature and the various attributes
          associated with it.

The FEATURID field is followed by a variable number of attribute fields
pertaining to the feature. Data descriptions and formats for each attribute
field are defined in the metadata for the geospatial database.

In addition to fixed format, fixed record length ASCII files, the BTS plans
to distribute attribute files in dBase format. Many existing GIS software
package can read dBase files directly, and this will obviate the need for
users of those packages to build import templates for each attribute file.

----------------------------------------------------------------------------

                                  Footnotes

[1] A seventh record type, Linear Reference, is still under development, but
will eventually be added to this set.

[2] A geospatial database may have more than one attribute or table file. The
two blank characters allow the BTS or users to establish a sequential
numbering scheme where multiple attribute files are linked to the same
geospatial feature.

[3] Starting and ending positions for links are generally determined by the
direction in which the link was digitized.

[4] In those cases where an area feature is composed of multiple polygons,
the CNTRLONG and CNTRLAT fields pertain to the centroid of each polygon.

================================================================================
