Description of TIGER System

Information in this description is drawn from the TIGER/Line(TM) file technical documentation[1]. The full document, in Adobe PDF format, along with sample data sets and other useful information, can be found at the TIGER home page. Here is a local copy of the Redistricting Census 2000 Tiger/Line File Technical Documentation. (This is the version of the data that we are using in our Map Server Demo.)


TIGER stands for Topologically Integrated Geographic Encoding and Referencing. The TIGER system was developed by the U.S. Bureau of the Census. The Bureau provides the public with the TIGER/Line files, which are ``extracts of selected geographic and cartographic information'' from the TIGER data base. Among other things, the Bureau also provides TIGER/SDTS(TM), which is ``a relational data file following the FIPS [Federal Information processing Standards] SDTS [Spatial Data Transfer Standard]''. This file contains ``data equivalent to the TIGER/Line files with additional relational data linkages and data content more similar to the Census TIGER data base.''

The TIGER/Line files are county-based, and they can be combined to cover the entire United States and its territories. They contain three types of data: line features, such as roads and railroads; landmarks, such as schools and parks; and polygon information for area boundaries. The line features and polygon information form the bulk of the data.

All latitude and longitude coordinates in the Tiger/Line files are given to six implied decimal places. The field width for latitude is 9 characters, including the sign (+/-), and the field width for longitude is 10 characters. Hence, the longitude values have room for three digits to the left of the (implied) decimal point. For example, ``-101795270+44090946'' represents the point with longitude -101.795270 and latitude 44.090946. The sources for the TIGER data include the USGS 1:100,000-scale Digital Line Graph, so the ``positional accuracy of the information is no greater than the established National Map Accuracy standards for 1:100,000-scale maps from the USGS (approximately +/- 167 feet)''. However, relative positions of the elements should be correct.

The TIGER data contains three kinds of geometric objects: points, polygonal lines, and polygons. The polygonal lines are called "complete chains". Each point is represented by a latitude/longitude pai, each complete chain is represented by a sequence of points, and each polygon is bounded by a sequence of complete chains. In addition, there is voluminous qualitative information associated with the geographic features, such as zip code, address range, etc. The following section gives a brief summary of how the data is stored in files.

Record Types

The data for a county may use up to 17 different record types, and all the records of a particular type are grouped together in a file. Not all record types will necessarily be used for every county. The Tiger/Line files are all ASCII, and each line represents one record, so the end-of-line character is also the end-of-record character. There are a constant number of fields for each record type, and each field in a record is a constant number of characters. If a field is missing, it will be filled with blanks (or zeroes, in the case of record type 2). What follows is a brief description of each record type.

Record Type 1
One record for each complete chain: its endpoints, feature class (e.g., local road), address ranges, zip codes, etc.
Record Type 2
Additional points for specifying the shape of those complete chains that are not straight line segments. Zero or more records for each complete chain.
Record Type 3
Voting district and other geographic information not included in record type 1. One record for each complete chain.
Record Type 4
Alternate feature name identifiers. Zero or more records for each complete chain.
Record Type 5
Map of alternate feature name identifier to alternate feature name.
Record Type 6
Additional address range and zip code data for street complete chains. Zero or more records for each complete chain.
Record Type 7
List of landmarks (e.g., hospitals, airports) associated with points and areas ("area landmarks" and "point landmarks"). Includes the point for point landmarks.
Record Type 8
Links of polygons to area landmarks. Zero or more records for each polygon; one or more records for each area landmark.
Record Type 9
Key geographic location features.
Record Type A
Geographic information (state, county, school district, etc.) for each polygon. One record for each polygon.
Record Type C
Geographic entity names.
Record Type H
TIGER/Line ID history.
Record Type I
Link complete chains to the polygons on either side. One record for each complete chain.
Record Type P
An internal point for each polygon. One record per polygon.
Record Type R
One record only, containing the range of allowable complete chain identifiers for this county.
Record Type S
Additional geographic information for each polygon. One record per polygon.
Record Type Z
US Postal service zip+4 codes.

Constructing Complete Chains

Record types 1 and 2 can be used to piece together all of the polygons in the county, and much of the other information as well. Each polygon is composed of one or more ``complete chains'', where each complete chain is a polygonal line. Complete chains may intersect only at their endpoints. Each complete chain serves on the border of two neighboring polygons, except for rare ``dead end'' chains, which have the same polygon on both sides. The endpoints of a complete chain are specified in record type 1, along with a unique Tiger/Line ID, or TLID. If the complete chain is not a straight line, then its intermediate points are specified in one or more records of type 2, which are linked to the chain's (single) record type 1 by the TLID. The only purpose of record type 2 is to store intermediate points, so not all chains need type 2 records.

In addition to the polyline endpoints, record type 1 contains many descriptive fields, including,

Many of these fields may be blank.

Here is a sample record of type 1, except that the spaces have been replaced with . characters, and the single line has been split into three lines, each ending with a \ character, to fit onto the page.


The first five characters give the record type (1) and version number (0024). The next ten characters represent the Tiger/Line ID, which is unique for each record of type 1. The following character holds a flag which indicates whether the line is single-sided. A single-sided line lies on the county boundary, so that the polygon on either its right or its left side is outside the county. In that case, certain fields, such as census tract and census block number, would be left blank for the side that is outside the county. The blank indicates that this line is not single-sided. The next character, B, is a code for the source of the data. Code B indicates USGS 1:100,000-Scale DLG-3 File. This is followed by a feature direction prefix (2 characters), a feature name (30 characters), a feature type (4 characters), and a feature direction suffix (2 characters); i.e., N. Front St. The three character code A31 is the census feature class code for Secondary and connecting road, State and county highways, unseparated. This is followed by four fields of eleven characters each representing the start and end addresses on either side of the line. The next four characters are impute flags for each address range endpoint. The impute flag indicates that an address range is based on calculations rather than known values. This can happen when a Tiger/Line is split (by a new road, for example), and it is not known at which point the address range was split. The next ten characters give the ZIP code on either side of the line (04357), and the ten characters after that (here blank) give codes for American Indian/Alaskan Native areas. The next two characters are flags for American Indian Trust Land, left and right side. And the two after that are for census internal use. This is followed by FIPS state code on either side (two characters each; 23 represents Maine), FIPS county code on either side (three characters each), and other FIPS codes for subdivisions and places (thirty characters total). Next are six characters each for the Census Tract number on either side (9801..), and four characters each for the Census Block number on either side (243. and 250.). Finally, the longitude and latitude coordinates for the start point and end point of the line. These coordinates have an implied decimal point, with six digits to the right of the decimal point. The longitudes have space for three digits to the left of the decimal point; the latitudes only need two.

Here is a sample record type 2, formatted in the same way.


Record type 2 also starts with the record type, version number, and Tiger/Line ID. This is followed by a three character field giving a sequence number, and ten fields for longitude and latitude of shape points. If fewer than ten shape points are needed, the remaining fields are padded with zeroes. If more than ten shape points are needed, then multiple records of type 2 will be given for that Tiger/Line, and numbered with the subsequent sequence number. The record shown has four shape points, and it is sequence number 1. Since there are no more shape points for this line, it will be the only record of type 2 for the line. A full line is a polygonal line from the start point in the record of type 1, to the shape points from any records of type 2, in order by sequence number and in order within the records, and finally to the end point from the type 1 record.

As an example, Sagadohoc County, Maine, contains 7540 type 1 records, and 5875 type 2 records.

Census Features Class Codes

The Census Feature Class Codes, which are used to describe line features in record type 1 and landmark features in record type 7, consist of three characters: a letter which identifies the feature class, a number which describes the major category, and a number describing the minor category. For example, the feature class code for the example line above is A31. The feature classes are

A. road,
B. railroad,
C. miscellaneous ground transportation,
D. landmark,
E. physical feature,
F. nonvisible features, and
H. hydrography.

Features that are unknown or not yet classified are given a code beginning with X. Either of the major or minor categories may be given a digit 0, indicating that the category is not known. This document describes the road feature class in detail, and the other classes cursorily.

There are seven major categories associated with the road feature class:

  1. primary highway with limited access or interstate highway;
  2. primary road without limited access, U.S. and State highway;
  3. secondary and connecting road, State and county highways;
  4. local, neighborhood, and rural road, city street;
  5. vehicular trail, road passable only by four-wheel drive vehicle;
  6. road with special characteristics;
  7. road as other thoroughfare.
The minor categories for all but the last two major categories are
  1. unseparated;
  2. unseparated, in tunnel;
  3. unseparated, underpassing;
  4. unseparated, with rail line in center;
  5. separated;
  6. separated, in tunnel;
  7. separated, underpassing;
  8. separated, with rail line in center.
So, for example, A31 represents Secondary and connecting road, State and county highways, unseparated, and A18 represents Primary road with limited access or interstate highway, separated, with rail line in center. The rail line in center minor categories include any situation where the railroad and road are both represented by one complete chain, even if the railroad is next to the road and not in center. None of the separated minor categories exist for the vehicular trail major category.

The last two major categories each have special minor categories. The road with special characteristics category includes cul-de-sacs, traffic circles, access ramps, service drives, and ferry crossings. The road as other thoroughfare category includes walkways, stairways, and alleys.

The railroad feature class includes the following major categories: railroad main line, railroad spur, railroad yard, railroad with special characteristics, and railroad as other thoroughfare. It includes the following minor categories: not in tunnel, in tunnel, and underpassing.

The miscellaneous ground transportation class includes pipelines, power transmission lines, tramways, monorails, and ski lifts.

The landmark feature class includes military installations, multihousehold or transient quarters, custodial facilities, educational or religious institutions, transportation terminals, employment centers, towers, and open space. Feature class codes for landmarks include, for example, D81 for Golf course and D36 for Jail or detention center.

Physical features include fences, ridges and mountain peaks.

Nonvisible features include such things as legal or administrative boundaries, property lines, and ZIP code boundaries.

The hydrography feature class contains the following major categories: naturally flowing water features (rivers and streams), man-made channel to transport water, inland body of water, man-made body of water, seaward body of water, body of water in a man-made excavation, nonvisible definition between water bodies, and special water features (e.g., glacier).


1. US Department of Commerce, Economics and Statistics Administration, Bureau of the Census, Washington, D.C. TIGER/Line(TM) Files, 1995 Technical Documentation, 1996.