EVOLUTION-MANAGER

Edit File: drv_tiger.html

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<title>U.S. Census TIGER/Line</title>
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<h1>U.S. Census TIGER/Line</h1>

TIGER/Line file sets are support for read access.  <p>

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. <p>

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.<p>

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

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

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

The reader was implemented for TIGER/Line 1998 files, but some effort has
gone into ensuring compatibility with 1992, 1995, 1997, 1999, 2000, 2002, 2003
and 2004 TIGER/Line products as well.  The 2005 products have also been
reported to work fine.  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.<p>

<h3>Feature Representation</h3>

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

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. <p>

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

<h4>CompleteChain</h4>

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.<p>

These features always have a line geometry.<p>

<h4>AltName</h4>

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. <p>

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. <P>