# U.S. Census TIGER/Line

TIGER/Line file sets are support for read access.

TIGER/Line files are a digital database of geographic features, such as roads, railroads, rivers, lakes, political boundaries, census statistical boundaries, etc. covering the entire United States. The data base contains information about these features such as their location in latitude and longitude, the name, the type of feature, address ranges for most streets, the geographic relationship to other features, and other related information. They are the public product created from the Census Bureau's TIGER (Topologically Integrated Geographic Encoding and Referencing) data base of geographic information. TIGER was developed at the Census Bureau to support the mapping and related geographic activities required by the decennial census and sample survey programs.

Note that the TIGER/Line product does not include census demographic statistics. Those are sold by the Census Bureau in a separate format (not directly supported by FME), but those statistics do relate back to census blocks in TIGER/Line files.

To open a TIGER/Line dataset, select the directory containing one or more sets of data files. The regions are counties, or county equivelents. Each county consists of a series of files with a common basename, and different extentions. For instance, county 1 in state 26 (Michigan) consists of the following file set in Tiger98.

    TGR26001.RT1
    TGR26001.RT2
    TGR26001.RT3
    TGR26001.RT4
    TGR26001.RT5
    TGR26001.RT6
    TGR26001.RT7
    TGR26001.RT8
    TGR26001.RT9
    TGR26001.RTA
    TGR26001.RTC
    TGR26001.RTH
    TGR26001.RTI
    TGR26001.RTP
    TGR26001.RTR
    TGR26001.RTS
    TGR26001.RTZ

The TIGER/Line coordinate system is hardcoded to NAD83 lat/long degrees. This should be appropriate for all recent years of TIGER/Line production.

There is no update or creation support in the TIGER/Line driver.

The reader was implemented for TIGER/Line 1998 files, but some effort has gone into ensuring compatibility with 1992, 1995, 1997, 1999, 2000 and 2002 TIGER/Line products as well. It is believe that any TIGER/Line product from the 1990's should work with the reader, with the possible loss of some version specific information.

### Feature Representation

With a few exceptions, a feature is created for each record of a TIGER/Line data file. Each file (ie. .RT1, .RTA) is translated to an appropriate OGR feature type, with attribute names matching those in the TIGER/Line product manual.

The TIGER/Line RT (record type), and VERSION attributes are generally discarded, but the MODULE attribute is added to each feature. The MODULE attribute contains the basename (eg. TGR26001) of the county module from which the feature originated. For some keys (such as LAND, POLYID, and CENID) this MODULE attribute is needed to make the key unique when the dataset (directory) consists of more than one county of data.

Following is a list of feature types, and their relationship to the TIGER/Line product.

#### CompleteChain

A CompleteChain is a polyline with an associated TLID (TIGER/Line ID). The CompleteChain features are established from a type 1 record (Complete Chain Basic Data Record), and if available it's associated type 3 record (Complete Chain Geographic Entity Codes). As well, any type 2 records (Complete Chain Shape Coordinates) available are used to fill in intermediate shape points on the arc. The TLID is the primary key, and is unique within the entire national TIGER/Line coverage.

These features always have a line geometry.

#### AltName

These features are derived from the type 4 record (Index to Alternate Feature Identifiers), and relate a TLID to 1 to 4 alternate feature name numbers (the FEAT attribute) which are kept separately as FeatureIds features. The standard reader pipeline attaches the names from the FeatureIds features as array attributes ALT_FEDIRS{}, ALT_FEDIRP{}, ALT_FENAME{} and ALT_FETYPE{}. The ALT_FENAME{} is a list of feature names associated with the TLID on the AltName feature.

Note that zero, one or more AltName records may exist for a given TLID, and each AltName record can contain between one and four alternate names. Because it is still very difficult to utilize AltName features to relate altername names to CompleteChains, it is anticipated that the standard reader pipeline for TIGER/Line files will be upgraded in the future, resulting in a simplification of alternate names.

These features have no associated geometry.

#### FeatureIds

These features are derived from type 5 (Complete Chain Feature Identifiers) records. Each feature contains a feature name (FENAME), and it's associated feature id code (FEAT). The FEAT attribute is the primary key, and is unique within the county module. FeatureIds have a one to many relationship with AltName features, and KeyFeatures features.

These features have no associated geometry.

#### ZipCodes

These features are derived from type 6 (Additional Address Range and ZIP Code Data) records. These features are intended to augment the ZIP Code information kept directly on CompleteChain features, and there is a many to one relationship between ZipCodes features and CompleteChain features.

These features have no associated geometry.

#### Landmarks

These features are derived from type 7 (Landmark Features) records. They relate to point, or area landmarks. For area landmarks there is a one to one relationship with an AreaLandmark record. The LAND attribute is the primary key, and is unique within the county module.

These features may have an associated point geometry. Landmarks associated with polygons will not have the polygon geometry attached. It would need to be collected (via the AreaLandmark feature) from a Polygon feature.

#### AreaLandmarks

These features are derived from type 8 (Polygons Linked to Area Landmarks) records. Each associates a Landmark feature (attribute LAND) with a Polygon feature (attribute POLYID). This feature has a many to many relationship with Polygon features.

These features have no associated geometry.

#### KeyFeatures

These features are derived from type 9 (Polygon Geographic Entity Codes) records. They may be associated with a FeatureIds feature (via the FEAT attribute), and a Polygon feature (via the POLYID attribute).

These features have no associated geometry.

#### Polygon

These features are derived from type A (Polygon Geographic Entity Codes) records and if available the related type S (Polygon Additional Geographic Entity Codes) records. The POLYID attribute is the primary key, uniquely identifying a polygon within a county module.

These features do not have any geometry associated with them as read by the OGR TIGER driver. It needs to be externally related using the PolyChainLink. The gdal/pymod/samples/tigerpoly.py script may be used to read a TIGER dataset and extract the polygon layer with geometry as a shapefile.

#### EntityNames

These features are derived from type C (Geographic Entity Names) records.

These features have no associated geometry.

#### IDHistory

These features are derived from type H (TIGER/Line ID History) records. They can be used to trace the splitting, merging, creation and deletion of CompleteChain features.

These features have no associated geometry.

#### PolyChainLink

These features are derived from type I (Link Between Complete Chains and Polygons) records. They are normally all consumed by the standard reader pipeline while attaching CompleteChain geometries to Polygon features to establish their polygon geometries. PolyChainLink features have a many to one relationship with Polygon features, and a one to one relationship with CompleteChain features.

These features have no associated geometry.

#### PIP

These features are derived from type P (Polygon Internal Point) records. They relate to a Polygon feature via the POLYID attribute, and can be used to establish an internal point for Polygon features.

These features have a point geometry.

#### ZipPlus4

These features are derived from type Z (ZIP+4 Codes) records. ZipPlus4 features have a many to one relationship with CompleteChain features.

These features have no associated geometry.

### See Also

- http://www.census.gov/geo/www/tiger/: More information on the TIGER/Line file format, and data product can be found on this U.S. Census web page.