Census Block Relationship Files
INTRODUCTION
The Census 2000 Block Relationship files are provided as a tool to help data users compare the universe of 1990 census blocks to the universe of Census 2000 blocks. From these files, data users may determine how 1990 blocks now relate to Census 2000 blocks and vice versa.
The data contained in the Relationship files is extracted from the Census Bureau's internal TIGER® database. The Census 2000 block relationship files portray the following relationships between the 1990 and the 2000 Census Blocks: 1990 Tabulation to 2000 Collection; 1990 Tabulation to 2000 Tabulation; and 2000 Collection to 2000 Tabulation.
The Census Bureau has provided relationship files to help data users meet their many and diverse needs. The majority of data users will need only the 1990 tabulation census block to Census 2000 tabulation block relationship file to see how 1990 tabulation blocks now correspond to Census 2000 blocks.
The Census 2000 Block Relationship Files were created for the 50 states, the District of Columbia, Puerto Rico and the following Island Areas: American Samoa, Guam, Northern Mariana Islands and the U.S. Virgin Islands.
Note: The 2000 collection blocks are the blocks used in the Census data collection phase by our Field staff. The 2000 tabulation blocks are the blocks used in the final data tabulations.
Census Block relationship files are organized into 3 types of relationship files:
CENSUS 2000 BLOCK RELATIONSHIP FILE FORMAT
Block relationship files are tabular files, they do not depict the actual spatial relationships between census blocks. Areal relationships between blocks can be determined by using commercially available GIS software and publicly available versions of the Census Bureau’s TIGER/Line files.
These block relationship files identify states and counties by FIPS (Federal Information Processing Standards) codes. These files do not include the geographic names referenced by the FIPS codes. Block relationship files are provided in a comma-delimited ASCII text file format. Each type of block relationship file has a separate record layout. The record layout for each type of relationship file is listed in the following section.
CENSUS 2000 BLOCK RELATIONSHIP RECORD LAYOUTS
1. 1990 Tabulation Census Block to Census 2000 Tabulation Block
| Field # | Maximum Length |
Field Description |
|---|---|---|
| 1 | 2 | 1990 tabulation state FIPS code |
| 2 | 3 | 1990 tabulation county FIPS code |
| 3 | 6 | 1990 census tract/BNA number & suffix |
| 4 | 4 | 1990 tabulation block number & suffix |
| 5 | 1 | 1990 tabulation block part flag |
| 6 | 2 | 2000 tabulation state FIPS code |
| 7 | 3 | 2000 tabulation county FIPS code |
| 8 | 6 | 2000 census tract number & suffix |
| 9 | 4 | 2000 tabulation block number |
| 10 | 1 | 2000 tabulation block part flag |
| Field # | Maximum Length |
Field Description |
|---|---|---|
| 1 | 2 | 1990 tabulation state FIPS code |
| 2 | 3 | 1990 tabulation county FIPS code |
| 3 | 6 | 1990 census tract/BNA number & suffix |
| 4 | 4 | 1990 tabulation census block number & suffix |
| 5 | 1 | 1990 tabulation census block part flag |
| 6 | 2 | 2000 collection state FIPS code |
| 7 | 3 | 2000 collection county FIPS code |
| 8 | 6 | 2000 collection block number & suffix |
| 9 | 1 | 2000 collection block part flag |
| Field # | Maximum Length |
Field Description |
|---|---|---|
| 1 | 2 | 2000 collection state FIPS code |
| 2 | 3 | 2000 collection county FIPS code |
| 3 | 6 | 2000 collection block number & suffix |
| 4 | 1 | 2000 collection block part flag |
| 5 | 2 | 2000 tabulation state FIPS code |
| 6 | 3 | 2000 tabulation county FIPS code |
| 7 | 6 | 2000 tabulation census tract number & suffix |
| 8 | 4 | 2000 tabulation block number |
| 9 | 1 | 2000 tabulation block part flag |
BLOCK PART FLAG
Block relationship files contain a part flag field associated with some 1990 and 2000 block numbers. The part flag is stored in the 1990 tabulation block part flag, and the 2000 tabulation block part flag fields of the record layouts. A value of "p" in any of these fields identifies block records that do not have a whole block to whole block relationship. The part flag indicator helps to explain the different types of relationships that exist between the block identifiers. The Census Bureau has created census block relationship information on the basis of one-to-one, one-to-many, many-to-one, and many-to-many block(s).
1. One-to-One Relationship
In some cases, a 1990 census block has a one-to-one relationship with a Census 2000 block.
Even though new block numbers have been assigned for Census 2000, the features used to define
Census 2000 blocks remain unchanged from 1990. This relationship is considered to be a one-to-one relationship.
For example, 1990 census block 101 (in census tract 16) has a one-to-one relationship with Census 2000 block 1000 (in census tract 16.01).
Example of a "one 1990 block-to one 2000 block" relationship:
11,001,001600,101,,11,001,001601,1000,
2. One-to-Many and Many-to-One Relationships
In a one-to-many relationship, a single 1990 census block is now represented by
more than one Census 2000 block. For example, 1990 block 102 (in census tract 16) is now
represented by Census 2000 blocks 1001 and 1002 (in census tract 16.01). The part flag
“p” indicates that only part of 1990 census block 102 is in each of the Census
2000 blocks 1001 and 1002.
11,001,001600,102,p,11,001,001601,1001,
11,001,001600,102,p,11,001,001601,1002,
In a many-to-one relationship, a number of 1990 census blocks may now be represented by only one Census 2000 block. For example, 1990 census blocks 103, 104, and 105 (in census tract 16) constitute Census 2000 block 1003 (in census tract 16.01).
Example of a "many 1990 blocks-to-one 2000 block" relationship:
11,001,001600,103,,11,001,001601,1003,p
11,001,001600,104,,11,001,001601,1003,p
11,001,001600,105,,11,001,001601,1003,p
3. Many-to-Many Relationship
A many-to-many relationship occurs when more than one 1990 census block is now represented by
more than one Census 2000 block. In this case, all 1990 census blocks and Census 2000 blocks in
question will have the part flag “p” associated with the block number. For example, 1990 census blocks 201,
202, and 203 (in census tract 16), are represented by Census 2000 blocks 5000, and 5001 (in census tract 16.01).
Example of a "many 1990 blocks-to-many 2000 blocks" relationship:
11,001,001600,201,p,11,001,001601,5000,p
11,001,001600,201,p,11,001,001601,5001,p
11,001,001600,202,p,11,001,001601,5000,p
11,001,001600,202,p,11,001,001601,5001,p
11,001,001600,203,p,11,001,001601,5000,p
11,001,001600,203,p,11,001,001601,5001,p
STATE AND COUNTY BOUNDARY CHANGES
The block relationship files are based on Census 2000 county boundaries. If there has been a change or correction to a state or county boundary, the 1990 census blocks associated with the change will be listed in the block relationship file for the state/county that gained territory. If a 1990 census block does not appear in the relationship file you expect to see it in, check all adjacent county files for that 1990 census block. Below are links to listing of counties that had a state or county boundary change or correction between the 1990 census and Census 2000. Changes are reported between counties using FIPS codes.
Appendix A of the Census 2000 TIGER/Line® Technical Documentation contains a listing of all State and County names
and their associated FIPS (Federal Information Processing Standards) Codes.
Select either
[PDF] or [Text] format.
FILE AVAILABILITY
The Census 2000 block relationship files are available to the public for download by individual county from the Census Bureau’s Web site. The relationship files are organized by type of relationship file, i.e. 1990 Tabulation Census Block to Census 2000 Tabulation Block.
1. 1990 Tabulation Census Block to Census 2000 Tabulation Block File
2. 1990 Tabulation Census Block to Census 2000 Collection Block File
3. Census 2000 Collection Block to Census 2000 Tabulation Block File
The Census Bureau plans to make the Census 2000 Block 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
If you have any questions regarding this product, please contact the Products and Services Staff of the Geography Division, U.S. Census Bureau by telephone: (301) 763-1128 or email: geography@geo.census.gov
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