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2010 Census Block Assignment Files Description


The Census Bureau's Redistricting Data Products provide the states and other data users with the small area census data necessary for legislative redistricting.  Among the geographic products disseminated for the 2010 Census are the Block Assignment Files (BAFs) and corresponding Name Look-up Tables (NLTs).

BAFs have been created for each of the 50 states, the District of Columbia, and Puerto Rico.  Each file contains 2010 Census tabulation block codes and geographic area codes for a specific geographic entity type.  Each BAF contains every block within the given state, even if the block is not within one of the geographic areas represented in the file.  For those blocks where no geographic area is present, the block is listed, followed by one or more commas (depending on the file layout for the specific geographic area type).

File Naming Convention

The file naming convention is as follows:


where <ss> is the 2-character state FIPS code, <USPSabbrev> is the 2-letter U.S. Postal Service (USPS) state abbreviation, and <entity> is the geography area type being represented.

File Format

BAFs are comma delimited text (.txt) files.  The first line of each BAF is the field header.  The 9 types of BAFs and the fields they contain are described below:

Geographic Area <entity> Field Layout
Congressional districts CD BLOCKID,DISTRICT
State legislative districts - upper SLDU BLOCKID,DISTRICT
State legislative districts - lower SLDL BLOCKID,DISTRICT
Elementary school districts SDELM BLOCKID,DISTRICT
Secondary school districts SDSEC BLOCKID,DISTRICT
Unified school districts SDUNI BLOCKID,DISTRICT
Incorporated places / census designated places INCPLACE_CDP BLOCKID,PLACEFP
American Indian / Alaska Native / Native Hawaiian areas AIANNH BLOCKID,AIANNHCE,COMPTYPE

Field Definitions

Field definitions are as follows:

  • BLOCKID:  15-character code that is the concatenation of fields consisting of the 2-character state FIPS code, the 3-character county FIPS code, the 6-character census tract code, and the 4-character tabulation block code.
  • DISTRICT:  variable length code representing the district (i.e., geographic area)
    • CD - 2-character code
    • SLDU - 3-character code
    • SLDL - 3-character code
    • VTD - variable length code of up to 6 characters
    • SDELM - 5-character code
    • SDSEC - 5-character code
    • SDUNI - 5-character code
  • PLACEFP:  5-character place FIPS code
  • AIANNHCE:  4-character American Indian / Alaska Native / Native Hawaiian (AIANNH) area census code
  • COMPTYPE:  1-character code indicating that if a block is within an AIANNH area, whether that area is represented as off-reservation trust land (T) or all other types (R).
  • COUNTYFP:  3-character county FIPS code

Source: U.S. Census Bureau | Geography | (301) 763-1128 |  Last Revised: December 06, 2012