Census Tract Relationship FilesOVERVIEW
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.
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:
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:
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 |
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 |
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: In some instances, various combinations of these four main relationships can exist.
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
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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
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3. Revision
These records show that 2000 census tract 414 includes a portion of 1990 census tract 415.
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
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Population-based example:
10001040200P 11735029610001040201 34771000 3477 9796DEKent 10001040200P 11735044210001040202 51891000 5189 32059DEKent 10001040200P 11735026210001040203 30691000 3069 59822DEKentStreet-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:
To download these files, select from the list of links below:
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American Samoa* |
Guam* |
Northern Mariana Islands* |
U.S. Virgin Islands* |
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
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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