Data Dictionary and Database Formats

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. 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. 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:Figure 1. If you are a user with a disability and cannot view this image, please call 800-853-1351 or email answers@bts.gov for further assistance.Figure 1.

Each geospatial database distributed by 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 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.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, 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 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. 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 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 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 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. 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, 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 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.