The TIGER system: A census bureau innovation serving data analysts

The TIGER System: A Census Bureau Innovation Serving Data Analysts

LARRY W. CARBAUGH* ROBERT W. MARX**

The U.S. Bureau of the Census has completed the initial development of the files underly-

ing its new automated geographic support system- the Topologically Integrated Geographic Encoding and Referencing System, or TIGER System. The first publicly available products from this effort-extracts from the TIGER database called the

TIGER/Line files-have been available in computer-readable form for the past 8 months,

and paper maps produced by the TIGER System have been mailed to every functioning

unit of local government in the United States within the past 4 months, including counties (and statistically equivalent areas), county subdivisions (townships, towns, and so

forth), incorporated places (cities, villages, and so forth), federally and state-recognized American Indian areas, and Alaska Native villages. The greatest potential opportunity

for applications outside the Census Bureau is for data analysts to use these files in con-

junction with the increasingly available technology called geographic information systems,

or GIS. Despite the magnitude of the accomplishment represented by the TIGER System, and the enormity of the potential applications for data analysts wishing to adopt GIS techniques, the Census Bureau has encountered substantial criticism recently because the content of the paper maps and the TIGER/Line files is not correct in every instance. In its continuing attempt to be responsive to the needs of its primary constituency- census data users-the Census Bureau has adopted a responsive policy regarding up-

date of the TIGER database with the corrections annotated by its field enumerators as well as those identified by local officials.

*Direct all correspondence regarding TIGER System extmcts to Larry W Carbaugh, ChieJ State and Regional

Progmms Staff, Data User Services Division, US. Bureau of the Census, Washington, D.C. 20233.

**Direct all corrspondence regarding TIGER System development and update plans to Robert W Marx, Chief; Geogmphy Division, US. Bureau of the Census, Ukrshington, D.C. 20233.

Government Information Quarterly, Volume 7, Number 3, pages 285-306. All rights of reproduction in any form reserved. ISSN: 0740-624X.

286 GOVERNMENT INFORMATION QUARTERLY Vol. ~/NO. 311990

The U.S. Bureau of the Census has a long history on innovation in the collection, processing, and dissemination of data, commencing with the first decennial census in 1790. Among the Census Bureau’s notable achievements are the first census data presentation using maps (the Statistical Atlas of the United States Based on the Results of the Ninth Census, MO), the use of mechanical tallying machines (the 1872 Seaton Device), the introduction of electronic machine tabulation (the 1890 Hollerith Machine), the introduction of scientific sampling techniques in census-taking (1940), the first major civilian use of a digital computer (UNIVAC-l, 1951), the development of a film optical sensing device for input to computers (FOSDIC, 1953), the first release of decennial census results to the public on computer tape (the Summary Tape Files, 1965), the development of the Address Coding Guides and the GBF/DIME System for assigning questionnaire addresses to geographic locations (1969), the application of computer graphics technology to support the Census Bureau’s data presentations (the Urban Atlas Series, 1975), and the “mastering” of a CD-ROM optical disk containing data from the 1980 Census of Population and Housing and the 1982 Census of Agriculture (1986).

Work on the 1990 census prompted development of another innovation-the TIGER System-that not only extends the Census Bureau’s impressive history of innovation but also provides data analysts with products containing information they can use with geographic information systems (GIS), computer mapping programs, and other geographically-oriented technologies. Using these automated tools, data analysts will be able to develop new techniques to examine environmental, transportation, and crime issues, to improve emergency and health services, to analyze markets, to determine legislative districts, and to utilize Census Bureau data and related geographic information for small areas to perform com- munity and neighborhood planning functions.

THE TIGER SYSTEM

The Bureau of the Census, in cooperation with the U.S. Geological Survey (USGS), developed the TIGER System to provide a nationwide digital map database that would be integrated with the geographic units used to support the Nation’s statistical programs,’ starting with the 1990 decennial census-the bicentennial census of the United States. TIGER is an acronym for Topologically Integrated Geographic Encoding and Referencing. Extracts from the TIGER database provide users of the Census Bureau’s statistical products with the information necessary to produce maps and to identify the political areas (such as cities and townships) and the statistical areas (such as census tracts and census blocks) that the Census Bureau will use to present the results of the 1990 census. Figure 1 provides a complete list of the geographic areas for which the Census Bureau tabulated data in its three most recent censuses, and for which it plans to tabulate the results of the 1990 decennial census.

TIGER Database Development

The Census Bureau derived the initial set of information in the TIGER database from two primary sources: the l:lOO,OOO-scale USGS maps and the Census Bureau’s GBF/DIME-Files?

The TlCER System: A Census Bureau fnnovation Serving Data Analysts 287

United States States and statisticaIly equivalent areas

states District of Columbia Outlying areas

Counties and statistically equivalent areas Minor civil divisions _ MCD Sub-MCDs Incorporated places American Indian reservations American Indian entities with trust lands Alaska Native villages - ANV AIaska Native Regional Corporations - ANRC Congressional districts Voting districts - VTD ZIP Codes School districts Neighborhoods

1 57 1 50

1 6’

3,231 30,450

265 19,176

278 37

209 12

435 36,361 37,000 E 16,075 28,381

STATISTICW

Regions Divisions Offshore areas Metropolitan areas

4 9

_-- ___

Standard consolidated statistical areas - SCSA 17 Consolidated metropolitan statistical areas - CMSA --- Standard metropolitan statistical areas - SMSA 323 Metropolitan statistical areas - MSA ___

Primary metropolitan statistical areas _ PMSA --- Urbanized areas - UA 373 Alaska Native village statistical areas - ANVSA (Sea ANV) Tribal jurisdiction statistical areas - TJSA ___

Tribal designated statistical areas - TDSA ___

County subdivisions 5,827 Census county divisions - CCD 5,512 Unorganized territories - UT 274 Other statistically equivalent areas 41 Special economic urban areas - SEUA ___

Census designated places - CDP 3,733 Balance of MSA ___

Census tracts 43,691 Block numbering areas - BNA 3,423 Block groups - BG 156,163

Tabulated parts 197,957 Enumeration districts - ED 102,235 Blocks 2,473,679

Tabulated parts 2,545,416

NUMBER OF ENTITIES*

1 57 2 50

1 62

3,248 30,410 E

145 19,500 E

310 E

(See ANVS;

E

1 55 3 50

1 43

3,221 ___ __.

6,776 6 --_ ___

12 ___

435 ___

90,000 E ___

40,000 E 31,000 E 16,000 E ___

40,000 E ___

4 9

_.. ___ _.. 21 ___

267 73

400 E 217

17 25

5,886 5,562

284 40 ___

4,000 E ___

50,000 E 11,400 E

234,000 E 357,500 E (See BG)

6,900,OOO g ___

1987 Censuses Economicculture

4 9 77

___ ___

21 ___

265 73 ___ --_ ___ ___

433 ___

___

433 s 44 g 34’0

___ ___ ___

1 53 4

50 __.

34 3,179 5

___ ___ _._ ___ ___ ___ ___ .__ -._

31,000 E __. __.

___ _._ _._

___ ___ ___ ___ ___ ___ ___ ___ ___

___ ___ _.. __. ___

___ __. ___

___ ___ ___

---Not applicable E = Estimated number * Numbers represent conditions as of December 31,1989

Figure 1. Geographic Tabulation Areas -- 1990 and Recent Censuses


figure 7. (Continued)

1 The 1980 decennial census included American Samoa, Guam, the Northern Mariana Islands, Puerto Rico, the Trust Territory of the Pacific Islands, and the Virgin Islands of the United States.

2 The 1990 decennial census will include American Samoa, Guam, the Northern Mariana Islands, Palau, Puerto Rico, and the Virgin Islands of the United States.

3 The 1987 economic censuses included Guam, the Northern Mariana Islands, Puerto Rico, and the Virgin Islands of the United States.

* The 1987 Census of Agriculture included Guam, Puerto Rico, and the Virgin Islands of the United States.

5 The 1987 Census of Agriculture aggregated the data for Alaska’s then 23 boroughs and census areas into 5 entities that it treated as the statistical equivalents of counties. That census did not provide separate data for independent cities, most counties that were coextensive with an incorporated place, and a few other counties and statistically equivalent areas.

6 The 1987 economic censuses included only those incorporated places having a population of 2,500 or more.

7 The 1987 economic censuses tabulated data for the seven offshore areas listed below, which they treat as the statistical equivalents of counties:

Alaska California Louisiana Texas

Atlantic Northern Gulf of Mexico Pacific

8 The 1987 economic censuses included only selected minor civil divisions in the six New England States.

9 Hawaii does not have incorporated places below the county level. In agreement with the Governor’s office, the decennial census tabulates the data for these areas as if they were incorporated places and the economic censuses tabulate data for them as CDPs.

IO The 1987 economic censuses aggregated the data for those portions of counties in the six New England States that were not included in some metropolitan area; they treat these areas as the statistical equivalents of places.

The TIGER System: A Census Bureau Innovation Serving Data Analysts 289

The CBF/DIME-Files

The GBF/DIME-Files were the basic source for the Nation’s major urban areas-covering less than 2 percent of the land area but 60 percent of the people in the United States. The majority of the GBF/DIME-Files-including those for all the urbanized areas that had been defined before the 1980 census-contained the features, feature names, and address ranges compiled by the local officials who helped the Census Bureau create those files over the course of 12 years and two decennial censuses. The Census Bureau presumed that this information was basically correct except for changes since the last update of these files in 1976. The Census Bureau created additional GBF/DIME-Files-58 of them, covering both urbanized areas defined as a result of the 1980 decennial census, and several other emerg- ing urban centers-between 1981 and 1985.

To prepare the GBF/DIME-Files for transformation into the TIGER database format and merger with the information that was being prepared as part of the cooperative project with the USGS, the Census Bureau updated the features (mostly streets) and feature names in the existing files and extended the feature network in all files to the boundaries of the immediately adjacent and partially-covered 1:24,000-scale USGS maps. This resulted in “squared-off’ GBF/DIME-Files that would align easily with the 1:100,000-scale information being developed in quadrangle format as part of the cooperative program with the USGS.

The l:lOO,OOO-Scale USGS Files

The cooperative program with the USGS provided the primary source for most3 of the remaining 9%plus percent of the Nation’s territory. The 1: lOO,OOO-scale maps of the USGS were compiled to National Map Accuracy Standards from mosaics of the appropriate 1:24,000-scale maps that had been reduced photographically to 1: 100,~scale? The feature information on the mosaics was updated using aerial photography that was no more than 3 years old at the time a particular map was prepared-and most were prepared during the 1983-1987 cooperative project period. This was in contrast to the 1980 census when the maps used for the 98-plus percent of the Nation outside the GBF/DIME-File areas were “the best the Census Bureau could find’loften local maps with compilation dates lo,24 or more years earlier. The USGS completed its portion of the cooperative program covering the lower 48 states and the District of Columbia4 by scanning their new 1: lOO,OOO-scale map sheets, editing the resulting data, and converting those data from raster image to vector f&rnat.5

The Census Bureau received four digital data files from the USGS for each 1: lOO,OOO-scale map: roads, railroads, hydrographic features, and miscellaneous transportation features. It “vertically integrated” these data files into a set of topologically consistent files based on the 1:24,000-scale map sheet boundaries (see Figure 2) to create the initial TIGER database. This process determined where roads crossed streams, railroads crossed rivers, roads intersected railroads, and so forth. These additional intersections became a permanent part of the database structure.

Updating for the 1990 Census

To make the information in the initial TIGER database more current for 1990 census operations, the geographic staff in the Census Bureau’s 12 regional offices collected the

290 GOVERNMENT INFORMATION QUARTERLY Vol. ~/NO. 3h990

Roads Hydrography

Integrated File

Railroads Miscellaneous

figure 2. Vertical Integration of U.S. Geological Survey Feature Files.

latest available maps from local officials across the United States. The geographic staff then compared the information shown on those locally-collected source maps with the information contained in the developing TIGER database. Where there were differences,

they inserted missing streets and street names, corrected obviously misaligned features, and used those locally-collected source maps to append names to all the roads that entered- the TIGER database from the USGS files; those files had come to the Census Bureau with no names. This work was done over a period of 4 years.

To complete the building of the TIGER database, the Census Bureau inserted the

geographic codes needed to identify the areas for which it collects and tabulates data. Cen- sus Bureau staff inserted the codes for both the 1980 decennial census and the 1990 decennial census to provide data analysts with the capability to compare, spatially, the results of these two “national snapshots.” This process included adding the additional lines needed to define the location of every geographic area boundary that did not follow some other mapped feature. All the operations involved in building the TIGER database received quality checks, using both visual inspection and computer edits, designed to keep the number of clerically-induced errors at “normal” levels?

At this stage in the process, the Census Bureau was ready to “horizontally integrate” the “squared-off’ and updated GBF/DIME-Files with the surrounding updated 1:100,000-scale files (or other appropriate tiles3). This process “tied together” the ends of the roads, railroads, rivers and other mapped features at the points where they crossed from file to file (map to map). Figure 3 illustrates the number of separate “pieces” that


went into this process. It also illustrates how the Census Bureau then “cut” these horizontally integrated files into the county units (and statistically equivalent areas) to be used as the basis for storing and further updating the TIGER database to support the data col-

lection and tabulation operations of the 1990 decennial census?

80” W

IGBF/DIME File !

Figure 3. Horizontal Integration of U.S. Geological Survey to Form County Units-Armstrong County, Pennsylvania.

-41” 30’ N

- 41”OO’N

1 40” 30’ N

Files and GBF/DIME-Files

292 GOVERNMENT INFORMATION QUARTERLY Vol. ~/NO. 3/1990

TIGER Database Description

The TIGER database provides digital data for all 1990 census map features and the associated geographic areas used for decennial census data collection (such as census blocks and census tracts) and tabulation (such as cities and townships) on both sides of each mapped feature. For most parts of the urbanized areas that were covered by the GBF/DIME- Files, the TIGER database also provides the address ranges and associated ZIP Codes on each side of all street segments. The TIGER database is in vector format.

The design of the TIGER database (see Figure 4) derived from the theories of topology, graph theory, and associated fields of mathematics! The geometric underpinnings of this database provide a mathematical description for the geographic structure of the United States that defines the location and relationship of streets, rivers, railroads, and other mapped features to each other and to the numerous geographic areas for which the Census Bureau tabulates the data from its censuses and sample surveys.

As Figure 4 illustrates, the TIGER database actually is many computer files linked together? This integrated structure simultaneously relates any change in the inventory of mappable features, address ranges, ZIP Codes, and geographic area codes in one component file to the related items in all other component files comprising the database. The info~tion about all features, along with the codes identifying the political and statistical areas for which the Census Bureau tabulates the data it collects, is stored as 0-, l-, and 2-cells. A O-cell represents a feature intersection or end point, but not intermediate points used to define a feature’s shape or other point locations; a l-cell represents a line connec- ting two O-cells; and a 2-cell represents the space (polygon) enclosed by a set of linked l-cells. The resulting computer database contains a latitude and longitude coordinate value for each of the more than 28 million feature inspections and end points that define the nearly 40 million feature segments that enclose the 12 million polygons in this giant “connect- the-dots” map of the United States and its possessions. One or a collection of 2-cells define each geographic area, including areas as small as a census block.

EXTRACTS FROM THE TIGER DATABASE

The component tiles of the TIGER datebase serve only internal Census Bureau purposes; they are not appropriate for “as is” delivery to the public. The Census Bureau is making the information in the TIGER database available to users through a series of phmned extract files.lO

TIGER/Line Files

In April 1988, the Census Bureau released its first extract product fmm the TIGER System, known as the Prototype TIGER/Line file. 11 This initial product was an extract from the TIGER database used to support the 1988 Dress Rehearsal Census of Boone County, Missouri. It was designed to allow users to become familiar with the TIGER/Line file format, to find out what they would like to see revised or improved in the file, and to allow vendors to develop applications software in advance of the plarmed fall 1988 release of a full set of extracts for the Nation and its possessions, to be known as the Precensus TIGER/Line files.

The TKER System: A Census Bureau Innovation Serving Data Analysts 293

Figure 4. The Census Bureau’s Internal TIGER Data Base Structure.

he response to the first Prototype TIGER/Line file was very positive, and demand for TIGER/Line files covering other counties mounted rapidly. The Census Bureau initially was able to respond to only the most urgent requests for Prototype TIGER/Line files covering additional counties, still planning for a fall 1988 release of the Precensus version. By late 1988, processing experience showed that the Precensus TIGER/Line files could not be ready until late 1989. To satisfy the public demand for TIGER database information, from February through April 1989 the Census Bureau released Prototype TIGER/Line files for all remaining counties and statistically equivalent areas in the Nation and its possessions. This gave anx-

ious data users an opportunity to examine the content of this new product for familiar areas and provide the Census Bureau with suggestions for improving the file’s format and content.

TIGER/Line File Data Description

As noted above, each TIGER/Line file is an extract of selected information from the Census Bureau’s internally maintained TIGER database. Each record in a TIGER/Line file represents a line feature traditionally found on a paper map, organized to form a topologically consistent line network. Each is classified by a code that describes the primary feature it represents, such as a road, a railroad, a river, or a statistical or political boundary. For example, if a line represents a road that also serves as the boundary for a city,

294 GOVERNMENT INFORMATION QUARTERLY Vol. ~/NO. 3/l990

the code will show only that the line is a road. To determine that the line also represents a city boundary, a TIGER/Line file user must check the left and right place code fields elsewhere in the record for this line.

The six record types that collectively comprise the TIGER/Line files contain geographic information (attributes) such as the name(s) of each feature, selected 1980 and 1990 census geographic area codes that pertain to each side of every feature, the latitude and longitude coordinate values defining the end points and shape of each feature, and the address ranges and ZIP Codes that apply to street segments in areas that had been covered by the GBFIDIME-Files.

The Census Bureau modified the format and content of the Prototype TIGER/Line files slightly when producing the Precensus TIGER/Line files. It did this in response to the comments received about the Prototype files. The Precensus TIGER/Line files correspond with the Precensus Local Review Maps that the Census Bureau sent to all functioning local governments. The following is a brief description of the Precensus TIGER/Line file record types?2

l Record ‘ljpe l-Basic Data Record provides a single record for each unique line segment in the TIGER/Line file. The end points of each line segment are expressed in latitude and longitude coordinate values. This record also contains the primary feature name, the address ranges, and ZIP Codes for street segments (in selected areas), and most 1990 census geographic area codes for each side of the line segment.

l Record Type 2-Shape Coordinate Points provides an additional series of latitude and longitude coordinate values that describe the shape of each line segment that is not straight.

l Record Type 3-Additional Decennial Census Geographic Area Codes includes some 1980 census geographic area codes and additional 1990 census geographic area codes. The 1980 census block numbers are included for areas covered by the GBF/DIME-Files.

l Record Type 4-Index to Alternate Feature Names provides an index to the alternate feature name(s) associated with those basic line segments in a county that have more than one commonly used name.

l Record Type %-Feature Name List contains a list of all unique feature names in the county.

l Record Type 6-Additional Address Range and ZIP Code Data provides additional address range and ZIP Code information in those instances in which all appropriate information for a side of a street segment cannot be presented as a single address range (that is, the house/building numbers are not arranged unitbrmly to form a single inclusive address range). Additional ZIP Codes, if more than one applies to a segment side, also appear.

Record lopes 1 and 3 contain the geographic keys to the Census Bureau’s statistical data-the data that are contained in the Summary Tape Files (STFs). These keys are the decennial census geographic area codes. Data analysts can use these geographic area codes and the associated statistical data for geographic information system (GIS) processing and display. Record Types 1 and 2 must be used together to graphically display the TIGER/Line file and do other spatial calculations. Without using the “shape” points provided in Record Type 2, some lines will appear to “cross” other lines when in reality they do not.


n Prototype El Precensus

<5 5-10 10-1.5 15-20 20-25 25-30 SO-35 35-40 40-50 50.60 60-70 TO>

File Size (Megabytes)

Figure 5. Distribution of TIGER/Line Files by File Size.

The geographic coverage for an individual TIGER/Line file is a county of statistically equivalent entity. The files can be combined to cover a state, a locally defined “region,” or the whole Nation. The files vary greatly in size, with some consuming less than .002

megal@e (Jemo Island, in the Marshall Islands) to one that requires over 100 megabytes (Los Angeles County, California); the average county consumes about 6 megabytes. Figure 5 shows the distribution of Prototype and Precensus TIGER/Line files by size category; the Precensus files are about 30 percent larger, on average, than the Prototype files, primarily because of the user-requested changes in record layout that the Census Bureau implemented.

Planned TIGER/Line File Versions

The Census Bureau plans to release additional TIGER/Line file extracts in the future- each representing the content of the TIGER database at the time the extracts are prepared. The Precensus version-the second-was released from October through December 1989. This version incorporated the file format and content improvements suggested by users

of the Prototype files, plus the updated codes that relate each polygon to the county, township, city, American Indian, and Alaska Native area in which it is located, as defined by the boundaries reported to the Census Bureau, primarily during the 1988 Boundary and Annexation Survey. (As noted earlier, for a data analyst to derive the complete boundary for a given political, administrative, or statistical entity, he or she must examine the left

and right code fields for that entity on each record.) The Precensus version also included updated street, street name, and address range information13 for the Nation’s urban centers derived from the resolution of initially unmatched addresses on the 1990 census mailing list.

Other planned releases of the TIGER/Line files include the Initial Voting District Codes version, scheduled for production from August through October 1990, and the 1990 Cen- sus version, scheduled for production in early 1991.


l The Initial Voting District Codes version will include the majority of the updated map features and feature names observed by Census Bureau en~e~~~ during their address list canvassing operations, as well as the majority of the corrections submitted by local officials participating in several 1990 census programs; this version also will contain the initial set of voting district codes that relate each 1990 census block to the voting district in which it is located, based on the boundaries submitted by officials in states participating in the 1990 Redistricting Data Program.

l The 1990 Census version will contain the geographic area codes that match the first detailed data tabulations from the 1990 census-the PL. 94-171 data file used for legislative redistricting. These codes represent the final 1990 census tabulation geography, which is based on January 1, 1990 political boundaries, and include the final set of voting districts in participating states. Figure 6 shows the four planned versions of the ~GE~Line fdes and the categories of info~ation each provides.

Version

Prototype

PK?Cl3lSUS

Initial Voting District Codes

1990 Census

Dates Available

Feb-Apr 1989

Oct.Dee 1989

Aug-Ott 1990

Jan-Mar 1991

vintage of Governmental

Unit Boundaries

1980

1980and1988

1980andlWO (Initial)

1980and1990 (Final)

Enumerator/ Local Official

Updates

No

No

Yes Prelist.Precanvassl

Local Official)

Yes WI Types)

Voting District Codes

NO

No

Yes (Initial)

Yes Pinal)

Figure 6. Planned Versions of the TIGER&ine Files

TlGE~Line File Availability

The cost to obtain copies of the TIGER/Line files is modest, in keeping with the Census Bureau’s policy to encourage the broadest possible use of its data and related products. The TIGER/Line files are available on computer tape. The price of the Precensus TIGER/Line files on computer tapes is $200.00 for the first county ordered in each state plus $25 for each additional county in that state ordered at the same time. At this price, the data set for the entire United States costs $87,450; including Puerto Rico and the other outlying areas, the cost is $9O,l50.

To support personal computer users, the Census Bureau is making the TIGER/Line files- beginning with the Precensus version-available on CD-ROM (Compact Disc-Read Only Memory). Each CD-ROM can store up to 550 megabytes of data. The discs are standard 4 3/4 W size and are compatible with all CD-ROM readers. The logical format of the data on the CD-ROMs uses the IS0 9660 standard, and the information is recorded as simple ASCII files. The price of the Precensus TIGER/Line files on CD-ROMs is $250.00 per disk, with the average disk containing 75-100 counties. The Census Bureau will release

The T/CER System: A Census Bureau innovation Serving Data Analysts 297

the initial Precensus TIGER/Line file CD-ROMs on a flow basis as it completes processing the files for a “disk-sized” group of counties. Once all counties are available, the Cen- sus Bureau plans to regroup the files to release state or regional CD-ROMs.

Tapes and CD-ROMs are sold by the Census Bureau’s Customer Services Branch, located in the Data User Services Division. Users in a hurry can order these products by telephone, but a major credit card (VISA or Master Card) is required. Deposit accounts also can be established. The Census Bureau’s Customer Services Branch can be reached at (301) 763-4100. In addition, many of the 54 State Data Centers-the data dissemination organiza-

tions cooperating with the Census Bureau in each state and four of the statistically equivalent areas-have obtained copies of the TIGER/Line files and are making them available for resale. The same is true for a number of private vendors.

Some limitations of TIGER/Line File Information

Coordinates-The coordinate information presented in the TIGER/Line files is provided for statistical analysis purposes only. It is only a graphic representation of ground truth. The positional accuracy of the information is no greater than established National Map Accuracy Standards for 1:100,000-scale maps from the U.S. Geological Survey for the features that entered the TIGER database from that source; the positioned accuracy of the information derived from the GBF/DIME-Files and other sources generally is of lower quality. Thus, the coordinated information in the TIGER/Line files is not suitable for high preci- sion measurement applications such as engineering requirements, property transfers, or other uses that might require highly accurate measurements of the earth’s surface. While the Census Bureau has made a reasonable and systematic attempt to gather the most recent information available about the accuracy and currency of the features that a file portrays, the Census Bureau cautions users that the files are no more complete than the source documents used in their compilation, the vintage of those source documents, and the transla- tion of the information on those source documents.

Address Ranges and ZIP Codes-The TIGER/Line files contain address ranges and their

associated ZIP Codes only for selected urban areas. The address range and ZIP Code information in the TIGER/Line files originated with the GBF/DIME-Files. The initial con- version of the GBF/DIME-Files to the TIGER database format involved neither any verification of the previously existing address range and ZIP Code information nor any significant updates or corrections to that information. The Prototype TIGER/Line files generally

reflected that status in the evolution of the TIGER database.‘3 The Census Bureau’s continuing preparations for the 1990 census involved making significant updates to the address range and ZIP Code information in the TIGER database for 20 GBF/DIME-File areas in- volving portions of 73 counties.‘4 In addition, the Census Bureau updated all TIGER database partitions containing former GBF/DIME-File coverage. It did this based on the research

of situations where the Census Bureau’s computers initially could not match the TIGER database to the addresses on the mailing list procured from the commercial vendors. This process involved adding new streets, new and corrected street names, new and revised address range information, and updated ZIP Code information in these areas.

298 GOVERNMENT INFORMATION QUARTERLY Vol. ~/NO. 3/l990

Other TIGER Extract Files

In addition to the TIGER/Line files, the Census Bureau plans to release several other TIGER extract products.

TIGERDataBase-these files will present the point, line, and area information in the Census Bureau’s internal TIGER database, rather than simply the linear features contained in the TIGER/Line files. These files will use the new national Spatial Data Transfer Standard (SDTS) format for digital cartographic data interchange, once it becomes official. The Census Bureau expects to release the TIGERDataBase version of the files in 1991.

TIGER/Boundary-these files will contain coordinate data for specific 1990 census tabulation area boundary sets; for example, a file containing all county boundaries, and another file containing all census tract and block numbering area boundaries. The Census Bureau expects to release these tiles in 1991.

TIGER/Comparability-this file will provide comparability information for 1980 and 1990 census tracts. The Census Bureau expects to release these files in 1991.

TIGERGICS-this file provides the geographic area names to link with the identifying geographic area codes for states, counties, minor civil divisions (townships, etc.) or census county divisions, and places contained in the various TIGER extract products. The Census Bureau plans to release a Precensus version of this file under the name Geographic Reference File-Names (GRFN) in early 1990 for $275, with a 1990 Census version to match the PL. 94-171 and Summary Tape File data tapes in 1991.

Assistance to Users

The Census Bureau will not be developing or distributing any software to support use of the TIGER/Line files; this task has been left to the private sector. Thus, for most data users, the quickest and easiest way to start using the TIGER System extracts is to obtain, from a vendor, software appropriate for the specific task envisioned and for the computer hardware available in the office where the files are to be used. More than 25 vendors- many of whom served data users in processing the Census Bureau’s 1980 census STFs and the TIGER/Line file’s predecessor, the GBF/DIME-Files-tell us they have the capability to manipulate and make use of the TIGER/Line files; a list appears as Figure 7. To obtain updates to this list, plus additional information about organizations that provide services for accessing and using information from the TIGER/Line files and other Census Bureau data products, the Census Bureau publishes a list called the National Clearinghouse for Census Data Services. A copy of the Clearinghouse list is available from the Customer Services Branch of the Data User Services Division; its telephone number is (301) 763-4100.

To provide information about its rapidly evolving and expanding list of data products, the Census Bureau operates an electronic bulletin board that provides up-to-date information on TIGER-related activities, such as new file releases and available public-domain software for use with the CD-ROM delivery of the files. This bulletin board provides a means for communicating with other TIGER/Line file users. The bulletin board is available 24 hours a day on (301) 763-1568.

The Census Bureau has been conducting workshops to inform data users about the TIGER/Line files and demonstrate some of the commercial software packages. The Census

The JKER System: A Census Bureau innovation Serving Data Analysts 299

Bureau also maintains a TIGER mailing list and plans to publish a newsletter featuring TIGER/Line file uses. Additional information about the TIGER System, training, and technical assistance is available from the Census Bureau’s regional census centers (see Figure

8) and from the agencies participating in the State Data Center Program; the regional census center staff can provide information about the State Data Center contacts.

Address Information Caliper Corporation

Mapping Services 4819 Cumberland Avenue

8403 Rockwood Lane Chevy Chase, MD 20815

(512) 454~AIMS (301) 654.4704

DeLonne Mapping Main Street

P.O. Box 298

Freeport, ME 04032

(207) 865.4171

Educational Data Systems, Inc.

901 Campisi Way, Suite 160

Campbell, CA 95008

(408) 559.4424

Environmental Science

Researrh Institute

380 New York Street

Redlands, CA 92373

(7 14) 793-2853

Et&, Incorporated

1430 O’Brien Drive

Menlo Park, CA 94025

(415) 328-3825

GeoBased Systems

12526 High Bluss Drive, Suite 160

San Diego, CA 92130

(619) 481-3119

Geographic Data Technology, Inc 13 Dartmouth College Highway

Lyme, NH 03768.9713

(603) 795.2183

GeoVision, Inc. 270 Scientific Drive, Suite One

Norcross, GA 30092

(404) 448.8224

Intergraph Corporation One Madison Industrial Park

Huntsville, AL 35807-4201

(205) 772-2222

McDonnell Douglas

7000 West Center Road, Suite 402 Omaha, NE 68106

(402) 391.2700

NOAAIOMA 34

Cameo Project

7600 Sand Point Way NE

Seattle, WA 98115

(206) 526.6319

Public Systems Awaciates, Inc.

303 E. 17th Avenue, Suite 440

Denver, CO 80203

(303) 831.1260

Sammamish Data Systems, Inc.

P.O. Box 70387

Bellevue, WA 98007

(206) 867-1485

Street Map Software

1014 Boston Circle

Schaumburg, IL 60193 (312) 529.4044

Synercom Technology, Inc.

2500 City West Boulevard, Suite 1100 1144 Daniel Webster Highway South

Houston, TX 77042 Suite 256

(713) 954-7000 Nashau, NH 03060

(603) 889.1800

U.S. statistics, Inc.

1101 King Street, Suite 601

Alexandria, VA 22314 (703) 979.9699

Wild System 9

373 Inverness Drive South, Suite 207

Englewood, CO 80112 (303) 799-9453

Contemporary Technology Corporation

3701 West Alabama, Suite 460

Houston, TX 77027

(713) 621.8166

Election Data Services

1522 K Street NW, Suite 626

Washington, DC 20005

(202) 789.2004

GENASYS, Inc.

2629 Redwing Road, #330

Fort Collins, CO 80526

(303) 226.3283

GeoVision Corporation

1600 Carling Avenue, Suite 350

Ottawa, Ontario KlZ 8R7

CANADA

(613) 722.9510

Maplnfo Corporation

200 Broadway

Troy, NY 12180

(518) 274.8673

Plangraphics, Inc.

202 West Main Street, Suite 200

Frankfort, KY 40601

(502) 223.1501

Strategic Mapping, Inc.

4030 Moorpark Avenue, Suite 250

San Jose, CA 95117.1848

(408) 985.7400

Figure Z Geographic Information System Vendors That Have Apprised the Census Bureau of Their Capability to Process TIGER/Line FilesJ5

300 GOVERNMENT INFORMATION QUARTERLY Vol. 7/No. 3h990

ATLANTA 1375 Peachtree Street NE 3rd Floor Atlanta, GA 30309-3112 (404) 347-5443

BOSTON Xew EngIand Power Building 44 1 Stuart street 4th Floor Boston, MA 02116-5000 (617) 421-1421

G~ARLU~~ 77 cor?3oFate Park Plaza 3410 S&t VardeII Lane Charlotte, NC 28217-1355 (704) 5214400

CIIICAGU Enterprise Center 2255 Enterprise Drive suite 5501 Westchester, IL 60154-5800 (312) 531-1990

DALLAS Exchange Place 6303 Harry Hines BouIevard Suite 210 Dallas, TX 75235-5228 (214) 767-7488

DENVER 6900 West Jef%rson Avenue Lakewood, CO 80235-2307 (303) 969-7750

DETROIT Signature Building 27300 West Eleven Mile Road suite 200 %.&&Id, MI 48034-2244 (313) 354-1990

.KAh’SAS CITY Tech Center *Building B 10332 NW Prairie View Road Box 901390 Kansas City, MO 64191.1390 (816) 891-7470

LOS ANGELES The Valley Corpnrate Park 16300 Roscoe Boulevard Buiiding 1 Van Nlrys, CA 91406-~2~~ (8181 904-6514

HEW YURR 221 west 41st street 16th Floor New York, NY 10036-7294 (212) 997-1990

441 North 5th street 3rd Ffoor Philndelphia, PA 19123-4090 (215) 597-1990

7 FRANCISCU 400 second StFeet 3rd Floor San Francisco, CA 94107-1400 (415) 974-9111

SEATTLE 101 Stewart street Suite 500 Seattle, WA 98101-1098 (206) 728.5300

Figure 8. The Census Bureau’s Regional Census Centers

HOW ARE THE Tl~~~~lN~ FItES BEING USEDl

Many uses of the informaGon in the TIGER/Line files are already taking place. Listed below are a few examples:

Emergency ~~~~~g-The National Oceanic and Atmospheric ~s~~on is using the TIGEWLine files as the map base for its CAMEO ~Compu~r-Aids Management of Emergency Operations) system. The tZAME0 software is designed to help emergency service organizations with their responses to chemical emergencies. The TIGER/Line file information was used at the national, state, and local level during the Valdez, Alaska oil spiIl and to assess damage in the aftermath of Hurricane Huga in 1989. Telephone companies and fire companies are using the TIGEWLme files as a framework for emergency 911 (E-911) operations. Routing and DehwySeveral businesses are usiug the TIGER/Line files to help plan delivery routes. Using the street name and address range information in the TIGER/Line files, they are locating delivery sites, dete rmining the best route to serve them, and the mileage between

The JlCER System: A Census Bureau innovation Serving Data Analysts 301

them. School administrators and waste disposal managers are using the information to track the movement of school buses and garbage trucks, respectively. Real Estate and Znsumnce Uses-A real estate firm added its multiple listing information to a TIGER/Line file-based system and offers this as a service to prospective home-buyers. It can now search the market for a desired home type and provide its customers with a map showing available units. Other Uses-TIGER/Line tile information is being studied by several states and private con- tractors to assist in realigning legislative districts to ensure that all districts will provide equal representation. TIGER/Line file information also is being used in several cities to monitor compliance with land use regulations and to evaluate tax payments and crime activity at various locations in these cities. Transportation planners are looking to use the TIGER/Line file information to inventory street signs, traffic lights, and road surfaces, and to analyze traffic accident locations.

Geographic Information Systems

The greatest potential for data analysts is to use the TIGER/Line files and the other TIGER System extract products in conjunction with the increasingly available technology called GIS. Because the TIGER System links the codes identifying the geographic areas for which the Census Bureau tabulates the data it collects directly with the underlying feature network, a GIS user can link the associated data sets that flow from the decennial, economic, and agriculture censuses to many other locally available data sets. In earlier decades, people described such uses as “thematic mapping,” and struggled to get the computer to help with the relatively limited data sets and geographic area outlines that were available in computer-readable form. In a GIS environment, and using the TIGER System extracts, a data analyst can examine numerous geographically distributed data sets-soil categories, hazardous wastes, water quality, land use/land cover, and so forth-in the context of the governments responsible for managing an area and the characteristics of the people who occupy the land, their homes, their farms, their businesses, and their industrial activity.

The geographic structure of the 1990 census, as documented in the TIGER System extracts, provides machine-usable units similar to the ones used by the people collecting and studying soils or land use/land cover information.

l There are more than 3,200 units generally known as counties. They provide fairly coarse resolution of the demographic characteristics describing the people and housing units in those counties. This level of detail is suitable mainly for large-area (national or regional) analysis and comparison.

l There are approximately 60,000 units of local government and statistically equivalent areas subdividing those 3,200-plus counties-townships, cities, villages, census county divisions, census designated places, and so forth. In addition, there are over 500 American Indian and. Ala&t Native areas. Together these units provide almost a twentyfold increase over counties in the number of tabulation units. Whole govem- mental units still offer fairly coarse resolution for a data analyst interested in studying a small area. On the plus side, demographic data are available for all these govem- mental units, and economic data are available for about the largest 20 percent.


l There are more than 60,000 census tracts and block numbering areas (BNAs) for the 1990 census-a significant increase over the number of these units in the 1980 census because now these areas cover the entire United States and its possessions.

l The census tracts and BNAs are subdivided into approximately 358,000 block groups that further segment the governmental units for purposes of data presentation. At this level, a GIS user has access to the full range of decennial census data-those items asked of every person and at every housing unit plus those asked at only a sample of housing units.

l Finally, for the 1990 census, the Census Bureau assigned block numbers nationwide. The result, once the governmental unit boundaries are superimposed, will be approximately 7 million census blocks for which there will be lOO-percent data tabulated following the 1990 census. As with the census tracts and BNAs, this represents a huge increase over the 1980 census when block-level data were available primarily for the urban cores of metropolitan areas and other incorporated places with a population of 10,000 or more.

The Census Bureau believes that the easy availability of the TIGER extract files, the low cost of the files, and the large number of processing systems and GIS packages available

commercially provide access to the power of this new product for nearly every potential useri Together with the data tapes that will be available following the 1990 census, and the data products available from the 1987 economic and agriculture censuses, the public has earned a wonderful return on its investment.

WHERE DOES THE TIGER SYSTEM GO FROM HERE?

One of the major results of any significant new program-and the Census Bureau believes that the TIGER System is one of these-is that people develop expectations of the product that far exceed the possible. The TIGER database has not been an exception. Thus, despite the tremendous accomplishment of developing this new automated geographic database for the entire United States and its possessions in only six years, some people were sur- prised and a few were very disappointed that the file was not perfect.

Errors in the TIGER Database

Based on the preliminary reports for a very small number of areas, the TIGER database does not contain records for some real streets, it contains records for some streets that do not exist, it contains some incorrect and mislabelled street names, it is missing some street names, and it contains some mistakes in the locations of the boundaries for the 1990 census.

To assess the extent of the problems in the first version of the TIGER File, as depicted

on the early map products used for 1990 census address list compilation and verification, the Census Bureau selected two samples of 1,000 blocks each from the areas included in the 1988 address listing operation (called “prelist” areas) and the 1989 address verification operation (called “precanvass” areas); the precanvass areas generally correspond to the areas covered by the GBF/DIME-Files. For both types of areas, Census Bureau field staff followed every street they found on the ground during the associated address listing/canvassing operations. They did this to compile and verify the 1990 census mailing list and


to correct the maps for the errors observed. Staff at Census Bureau Headquarters examin- ed the annotated maps resulting from these “on-the-ground” observations and compiled the preliminary results shown in Figure 9: the results show that nearly 68 percent of the

blocks in the 1988 prelist area sample and over 86 percent of the blocks in the precanvass area sample contain no enumerator-noted corrections whatsoever.

Prelist ibeas

r Percent

Total number of sample blocks Loo0 17

Number of blocks available for review Number of non-annotated blocks Number of annotated blocks

987 668 319

Total number of segments Average number of segments per block Number of annotated segments Average number of annotated

segments per block

7,952 8.06

1,379

Blocks requiring 1 correction Total segments affected

Blocks requiring 2 corrections Total segments affected

Blocks requiring 3 or more corrections Total segments affected

Blocks having critical errors Total segments affected

1.40

121 121

72 134

126 1,124

3 7

67.68 32.32

17.34

12.26 1.52

7.29 1.69

12.77 14.13

0.30 0.09

Precanvass Areu

Number

1,006

946 816 130

5,897 6.23 325

0.34

Percent

86.26 13.74

5.51

53 5.60 53 0.90

42 4.44 73 1.24

35 3.70 199 3.37

3 0.32 4 0.06

Figure 9. Results of the 2,000 Block Sample Analysis.

The rather large numbers of corrections identified by the Census Bureau’s field staff-as revealed by the sample analysis-appear to have resulted at least partially from some deti- ciencies in the local source materials used during the TIGER database-building process. This seems especially likely in the case of feature deletions, many of which probably were “paper streets” on the local source maps, a common problem with many “official” maps. The principal explanation for the feature additions appears to be growth that took place after the local source maps were compiled and the initial TIGER database was built; the bulldozers did not stop scraping out new streets in rapidly growing areas just because the Census Bureau had completed one phase of its TIGER database updating operation.

Near-Term TIGER Database Updates

The Census Bureau’s original plan was to make most further corrections to the features and feature names in the TIGER database following the completion of the 1990 census.


The only corrections the Census Bureau planned to enter in 1989 and 1990 were “critical” errors identified by its enumerators-items such as a land area shown as water, an area

where every street name was incorrect or “attached” to the wrong line, and so forth. While

the 1990 census planners knew that the maps produced from the TIGER database would

contain some errors of the type described above, they also knew that the procedures they had prepared for the prelisters, precanvassers, and followup enumerators provided the means to make their maps and the related 1990 census data correct, thus overcoming any errors in the TIGER database that might otherwise affect enumeration accuracy.

Strong data user interest in having maps that displayed these corrections, coupled with the unexpected availability of extra machine resources (because of the continued presence of graphic work stations scheduled for replacement by new devices), led the Census Bureau to decide to enter the enumerator-noted corrections, plus those brought to its attention by

local officials, during the fall/winter of 1989 and the winter/spring of 1990. By doing this,

the Census Bureau can produce maps for the postcensus phase of its Local Review Pro- gram that will depict the complete set of features its field staff saw as they completed their address list compilation and verification work. These same improvements in map content will benefit all other users of the maps and the TIGER System extract products as well- marketers, redistricters, delivery routing managers, emergency service personnel, and so forth.

The Future

The feature network of the United States will continue to change as the Nation grows and the settlement pattern evolves further from the agrarian past to the urban future. The Census Bureau intends to maintain its investment in the TIGER database by updating the information as needed to support the future statistical programs of the Federal government, starting with the 1992 economic and agriculture censuses and the redesign of the sample areas the Census Bureau uses to compile monthly, quarterly, and annual indicators about the people and institutions of this great Nation.

The structure of the TIGER database and the methodology used likely will change as the Census Bureau evaluates the results of the 1990 census process and considers the wealth of new computer-readable map sources that other Federal agencies, state and local govem- ments, and private-sector firms have developed recently. To prepare for this future work, the Census Bureau has begun the process of exploring available resources, discussing potential cooperative arrangements with other agencies and organizations, and working with dedicated experts to develop and implement standards that will enhance the ability of everyone to accomplish digital map data exchanges in a cost-effective and timely manner. This process likely will involve some who read this article. The Census Bureau welcomes your ideas and suggestions.

NOTES AND REFERENCES

1. Robert W. Marx, “The TIGER System: Automating the Geographic Structure of the United States Census,”

Govemmenr Publications Review, l3 (1986): 181-201.

2. Joel Sobel, “Principal Components of the Census Bureau’s TIGER File,” Research in Contemporary and

Applied Geogmphy: A Discussion Series, 10 (1986): 1-16.

3. The 1: lOO,OOO-scale USGS maps cover the lower-48 states plus the District of Columbia (which also is

covered by a GBF/DIME-File that served as the primary source for the features in Washington, D.C.


4.

8

9.

10.

11.

12.

l3.

14.

metropolitan area). To complete the coverage of the United States and its possessions-including Puerto

Rico, the Virgin Islands of the United States, Guam, American Samoa, the Northern Mariana Islands, Palau,

and the other areas comprising the former Trust Territory of the Pacific Islands-Census Bureau staff digitized

maps directly. Generally these were larger-scale (1:24,000 and 1:2O,ooO-scale) USGS maps, but some were

smaller-scale (1:250,000-scale) USGS maps for areas such as the remote portions of Alaska.

Bruce Y. McKenzie and Robert A. LaMacchia, “The U.S. Geological Survey-U.S. Bureau of the Census

Cooperative Digital Mapping Project: A Unique Success Story,” paper presented at the fall meeting of the

American Congress on Surveying and Mapping in Reno, Nevada, 1987.

“1:1OO,OOO-Scale Digital Cartographic Database for Federal Requirements,” United Stares Geological Survey

Yearbook, Fiscal Year 1984 (Reston, VA, 1985), pp. 4-12.

Robert W. Marx and Alan .I. Saalfeld, “Programs for Assuring Map Quality at the Bureau of the Census,”

Proceedings of the 4th Annual Research Conference (Washington, D.C., 1988), pp. 239-259. Robert W. Marx, “The TIGER Syste.m: Six Years to Success,” Proceedings: 13th International Conference

ofrhe In~emationul Cartographic Association (Morelia, Mexico, 1987), pp. 633-645; and Robert W. Marx

(editor), et al., “The Census Bureau’s TIGER System,” a special content issue of Gzrtogmphy and Geogmphic

Information Systems, 17 (NW).

Gemrd Boudriaulr, “Topology in the TIGER File,” Proceedings: Eighth International Symposium on Com- puter Assisted Cartogmphy (Falls Church, VA, 1987), pp. 258-263.

Christine Kinnear, “The TIGER Structure,” Proceedings: Eighth Inrernational Symposium on Computer

Assisted Cartogmphy (Falls Church, VA, 1987), pp. 249-257.

Robert A. LaMacchia, Silla G. Tomasi, and Sheldon K. Piepenburg, “The TIGER File: Proposed Pro-

ducts,” paper distributed at the fall meeting of the National Conference of State Legislatures in Hartford,

COMCCtiCUt, 1987.

“TIGER/Line Prototype Files, 1990 Technical Documentation,” U.S. Bureau of the Census (Washington,

D.C., 1989). “TIGER/Line Precensus Files, 1990 Technical Documentation,” U.S. Bureau of the Census (Washington,

DC., 1989).

For 233 counties, the sequence of TIGER database update and Prototype TIGER/Line file extract opera-

tions resulted in the Prototype files containing the address range and ZIP Code updates described for the

Precensus TIGER/Line files. Purchasers of the listed Prototype files who are using them only for matching

address lists to 1990 census block numbers will not gain any improvement using the Precensus TIGER/Line

files.

The Census Bureau made extensive additions to the address range and ZIP Code information in the TIGER

database for the counties listed below (grouped by GBF/DIME-File) because doing so allowed it to com-

plete coverage for the major city(ies) in the area or to include a significant number of additional housing

units (generally 100,000 or more) in the automated address list matching operation.

Atlanta, GA Plymouth, MA Denton, TX

Clayton, GA Worcester, MA Johnson, TX Cobb, GA Chicago, IL Parker, TX Douglas, GA DuFage, IL Rockwall, TX Fayette, GA Kane, IL Tarrant, TX

F&on, GA Kendall, IL Fall River, MA-RI

Gwinnett, GA Lake, IL Bristol, MA

Henry, GA McHenry, IL Newport, FU

Rockdale, GA Will, IL Gary-Hammond, IN

Baltimore, MD Cincinnati, OH-KY Lake, IN

Carroll, MD Clermont, OH Porter, IN Harford, MD Warren, OH Houston, TX

Boston, MA Boone, KY Bramria, TX

Bristol, MA Campbell, KY Fort Bend, TX Essex, MA Kenton, KY Harris, TX Middlesex, MA Dallas-Fort Worth, TX Lakeland-Winter Haven, FL

Norfolk, MA Collin, TX Polk, FL


Long Branch-Ashury Park,NJ Monmouth, NJ Ocean, NJ

Los Angeles, CA Los Angeles, CA

Mlnnenpolls-St Paul, MN

Anoka, MN

Carver, MN

Dakota, MN

Hennepin, MN

Scott, MN

Washington, MN

Nassau-Suffolk, NY

Suffolk, NY

New York, NY-NJ

Westchester, NY

Bergen, NJ

Paterson, NJ

Passaic, NJ

Philadelphia, PA-NJ

Bucks, PA

Chester, PA

Delaware, PA

Montgomery, PA

Burlington, NJ

Camden, NJ

Gloucester, NJ

Pittsburgh, PA

Allegheny, PA

Beaver, PA

Westmoreland, PA

Providence, RI-MA Bristol, RI

Kent, RI

Providence, RI

Washington, RI

Bristol, MA

Norfolk, MA

Worcester, MA

Riverside-San Bernardino, CA Riverside. CA

15. Information provided as of January 2, 1990.

16. Robert W. Marx, “LIS/GIS Activities of the United States Census Bureau,” paper presented at an informa-

tion exchange sponsored by the United States Embassy in Bonn, Federal Republic of Germany, 1988.

17. Maps were missing from the enumerator assignment package for some sample blocks. The remaining statistics

are based on the number of blocks available for review.

Documents

The TIGER system: A census bureau innovation serving data analysts