Census 2000 Census Tract Relationship Files

Census Tract Relationship Files

OVERVIEW

As part of the Census 2000 geographic product series, the Census Bureau has produced Census Tract Relationship Files. (In previous censuses, this product was called a comparability file.) These files show how 1990 census tracts relate to Census 2000 census tracts. The files consist of one record per each 1990 census tract/2000 census tract spatial set. A spatial census tract set is defined as the area that is uniquely shared between a 1990 census tract and a 2000 census tract.

The Census Tract Relationship Files consist of four sets of files. The purpose of these files is to assist users in determining the relationships between 1990 and 2000 census tracts. Two of these files are state-level entity based census tract relationship files. One file provides a measurement of change based on population; a second measures change using street-side mileage. The other two files specifically list census tracts that have experienced significant change: one file from the perspective of 1990 census tracts, the other from the perspective of Census 2000. All four census tract relationship files will be available for each state-level entity as well as at the national level.

The Census 2000 census tract relationship files are in fixed length ASCII format. The two census tract relationship files consist of one record per each 1990 census tract/2000 census tract spatial set. A spatial census tract set is defined as the area that is uniquely shared between a 1990 census tract and a 2000 census tract. The two files of significantly changed census tracts consist only of a list of census tracts that exhibited a change of 2.5-percent or greater. The current release includes 56 sets of files, one set for each of the 50 states plus separate files for the District of Columbia, Puerto Rico, American Samoa, Guam, the Northern Mariana Islands, and the U.S. Virgin Islands.

FILE DESCRIPTIONS

1. Population-based Census Tract Relationship Files
As stated above, each state-level entity file is comprised of a record for each unique spatial 1990/2000 census tract area combination within the state. In addition to the 1990 and 2000 census tract codes, each record contains three population figures; the Census 2000 population for the record, the Census 2000 population for the entire 2000 census tract, and the actual or estimated Census 2000 population for the area of the 1990 census tract (not the 1990 population for the 1990 census tract). Also, to identify changes and the proportion of change, the record includes "part" indicators for both the 1990 and 2000 census tracts, and the percent of the Census 2000 population represented for the 1990 and 2000 census tracts represented in that record.

Note: As part of the procedure to provide 2000 population data for 1990 census tracts, the Census Bureau has rounded the Census 2000 tabulation block population data for some of the blocks that are split by 1990 census tract boundaries. This rounding procedure may create individual census tract, county, and/or state population totals that are slightly different from the official Census 2000 population totals. Also, the Census 2000 population for the 1990 census tract and for the record is an estimate for each 1990 census tract that had a 1990 boundary not identical to a Census 2000 census block boundary.

2. Street-side Mileage-based Census Tract Relationship Files
This file type is almost identical to the population-based census tract relationship files, except that these files use street-side mileage, rather than population, as a means to measure relationship. Please refer to the following PDF document for an illustrated explanation of how street-side mileage is calculated: calculating street-side mileage or the alternate [text] version.

3. Significantly Changed 1990 Census Tracts Files
This file type lists ¹ those 1990 census tracts that have exhibited a change of 2.5-percent or more for 2000. It uses the data contained in the population-based census tract relationship file.

Note: The amount of change of 2.5-percent or greater can reflect either a sum of gain or loss of Census 2000 population within a given census tract.

4. Significantly Changed 2000 Census Tracts Files
This file type lists ¹ all 2000 census tracts that had more than 2.5-percent of their Census 2000 population in a different 1990 census tract.

Note: This file was generated by using the national population-based file to identify all 2000 census tracts that did not have 97.5% of their population in a 1990 census tract with the same number.

FEDERAL INFORMATION PROCESSING STANDARDS (FIPS) CODES

The FIPS assigned to the state-level and county-level entities for Census 2000 are codes located in Appendix A of the TIGER/Line^® Technical Documentation:

[PDF] version; [Text] version.

For a list of FIPS Codes assigned to state-level and county-level entities at the time of the 1990 Census, please use Appendix A of the 1990 TIGER/Line Technical Documentation:

[PDF] version; [Text] version.

RELATIONSHIP FILE RECORD LAYOUTS

Record Layout for the Population-based Census Tract Relationship File

Field	Field Length	Field Description
1-2	2	1990 state FIPS code
3-5	3	1990 county FIPS code
6-9	4	1990 census tract base
10-11	2	1990 census tract suffix
12	1	1990 census tract part flag
13-21	9	Census 2000 population for 1990 census tract
22-25	4	Percentage of 1990 census tract population^*
26-27	2	2000 state FIPS code
28-30	3	2000 county FIPS code
31-34	4	2000 census tract base
35-36	2	2000 census tract suffix
37	1	2000 census tract part flag
38-46	9	Census 2000 Population of 2000 census tract
47-50	4	Percentage of 2000 census tract population^*
51-59	9	2000 population of the area covered by the record
60-73	14	Land area of the record (1000 sq.meters)
74-75	2	2000 state name abbreviation
76-135	60	2000 county name

^*These figures are shown to one decimal place (000.1); the decimal place is implied.

Record Layout for the Street-side Mileage-based Census Tract Relationship File

Field	Field Length	Field Description
1-2	2	1990 state FIPS code
3-5	3	1990 county FIPS code
6-9	4	1990 census tract base
10-11	2	1990 census tract suffix
12	1	1990 census tract part flag
13-18	6	Street-side mileage of 1990 census tract
19-22	4	Percentage of 1990 census tract street-side mileage^*
23-24	2	2000 state FIPS code
25-27	3	2000 county FIPS code
28-31	4	2000 census tract base
32-33	2	2000 census tract suffix
34	1	2000 census tract part flag
35-40	6	Street-side mileage of 2000 census tract
41-44	4	Percentage of 2000 census tract street-side mileage^*
45-50	6	Street-side mileage of the area covered by the record
51-64	14	Land area of the record (1000 sq.meters)
65-66	2	2000 state name abbreviation
67-126	60	2000 county name

^*These figures are shown to one decimal place (000.1); the decimal place is implied.

Record Layout for the Significantly Changed 1990 Census Tracts File

Field	Field Length	Field Description
1-2	2	1990 state FIPS code
3-5	3	1990 county FIPS code
6-9	4	1990 census tract base
10-11	2	1990 census tract suffix

Record Layout for the Significantly Changed 2000 Census Tracts File

Field	Field Length	Field Description
1-2	2	2000 state FIPS code
3-5	3	2000 county FIPS code
6-9	4	2000 census tract base
10-11	2	2000 census tract suffix

TYPES OF CENSUS TRACT RELATIONSHIPS

Within the population-based and street-side mileage-based census tract relationship files for Census 2000, there are four main types of census tract relationships that occur: no change, merge, revision, and split.

Note

Examples of the four main census tract relationship types are provided below for both the street-side mileage and population-based census tract relationship files for Kent County, Delaware.

1. No Change
This record is an example of a census tract (401) that exhibited no change from 1990 to 2000.
Note: Both percentages are 100-percent and there are no "P" part indicators.

Population-based example:

10001040100    5337100010001040100    53371000    5337    124644DEKent

Street-side mileage-based example:

10001040100    2036100010001040100    20361000    2036   124644DEKent

2. Merge
These records show that 1990 census tracts 403 and 404 merged to form 2000 census tract 404.
Note: The effect of rounding shows up in these records. The sum of the population for each record (824 and 823) does not equal the population of the 2000 census tract (1,648). (Refer to the note on rounding in the "File Descriptions" section, under the heading "1. Population-based Census Tract Relationship File.")

Population-based example:

10001040300    172100010001040400P    11560149    172     77556DEKent
10001040400    984100010001040400P    11560851    984    100528DEKent

Street-side mileage-based example:

10001040300    824100010001040400P    16480500    824     77556DEKent
10001040400    823100010001040400P    16480500    823    100528DEKent

3. Revision

Population-based example:

10001041400     3008100010001041400P    30180997    3008    6671DEKent
10001041500P    3799000310001041400P    30180003      10     110DEKent
10001041500P    3799099710001041500     37891000    3789    3068DEkent

Street-side mileage-based example:

10001041400     350100010001041400P    3650958    350    6671DEKent
10001041500P    310004910001041400P    3650042     15     110DEKent
10001041500P    310095110001041500     2941000    294    3068DEKent

4. Split:

Population-based example:

10001040200P    11735029610001040201    34771000    3477     9796DEKent
10001040200P    11735044210001040202    51891000    5189    32059DEKent
10001040200P    11735026210001040203    30691000    3069    59822DEKent

Street-side mileage-based example:

10001040200P    2987021110001040201     6311000     631     9796DEKent
10001040200P    2987036310001040202    10851000    1085    32059DEKent
10001040200P    2987042610001040203    12721000    1272    59822DEKent

CENSUS 2000 CENSUS TRACT RELATIONSHIP FILE AVAILABILITY

Each state folder will contain four census tract relationship file types. The file naming convention is: "xx" represents the 2-character Post Office state abbreviation, and "NN" represents the 2-digit state FIPS code:

xxNNpop.txt - Population-based Census Tract Relationship File
xxNNsg2k.txt - Significantly Changed 2000 Census Tracts File
xxNNsg90.txt - Significantly Changed 1990 Census Tracts File
xxNNssm.txt - Street-side Mileage-based Census Tract Relationship File

To download these files, select from the list of links below:

Alabama	Kentucky	Ohio
Alaska	Louisiana	Oklahoma
Arizona	Maine	Oregon
Arkansas	Maryland	Pennsylvania
California	Massachusetts	Puerto Rico
Colorado	Michigan	Rhode Island
Connecticut	Minnesota	South Carolina
Delaware	Mississippi	South Dakota
District of Columbia	Missouri	Tennessee
Florida	Montana	Texas
Georgia	Nebraska	Utah
Hawaii	Nevada	Vermont
Idaho	New Hampshire	Virginia
Illinois	New Jersey	Washington
Indiana	New Mexico	West Virginia
Iowa	New York	Wisconsin
Kansas	North Carolina	Wyoming
	North Dakota
American Samoa*	Guam*	Northern Mariana Islands*
		U.S. Virgin Islands*
		National files

The Census Bureau plans to make the Census 2000 Census Tract Relationship Files available for purchase on CD-ROM. No precise release date has been established at this time. Once the files are available on CD-ROM, ordering information will be accessible from our online catalog, URL: http://www.census.gov/mp/www/censtore.html

USER NOTES

These measurements are recorded in thousands of square meters.
To convert square meters (in thousands) to square miles divide by 2589.988.

To obtain total land area for a census tract, use the geographic header file in the Census 2000 Summary File 1 (SF1). Refer to the SF1 README file for instructions on accessing and using the geographic header file.

¹ In both the 1990 and 2000 Significantly Changed Census Tract Files,
the associated state and county FIPS (Federal Information Processing 
Standards) Codes appear before each census tract number. For example,
census tract 402.01, located in Kent county, Delaware exhibited a 
change of 2.5-percent or greater for 2000. Therefore, in the Census 
2000 significantly changed census tract file its entry is 10001040201; 
where 10 is the FIPS state code for Delaware, 001 is the FIPS county 
code for Kent county, and 040201 is the census tract number.

Return to census tract file descriptions

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Source: U.S. Census Bureau
Created: August 10, 2001
Last Revised: Friday, 10-Sep-2004 10:31:59 EDT

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