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.

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

1990 Tabulation Census Block to Census 2000 Collection 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 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

Census 2000 Collection Block to Census 2000 Tabulation Block

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