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Background

Building Blocks The process of creating decennial census tabulation blocks. GeoElections User’s Conference October 6 th , 2011 Tampa, Florida. Background. Census Block

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Background

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  1. Building BlocksThe process of creating decennial census tabulation blocks.GeoElections User’s ConferenceOctober 6th, 2011Tampa, Florida

  2. Background • Census Block • The smallest entity for which the Census Bureau collects and tabulates decennial census information; bounded on all sides by visible and nonvisible features shown on Census Bureau maps.

  3. Background • Enumeration Districts (EDs)–1870 to 1980 • 1870 - Maximum size of sub-districts for enumeration lowered from 50,000 to 6,000 • 1880 – Maximum size of sub-districts for enumeration lowered from 6,000 to 4,000 • 1910 – began using legally or administratively defined entities for EDs • 1940 – Blocks introduced for larger places

  4. Background • Enumeration Districts (EDs)–1870 to 1980 • 1940 – Blocks introduced for larger places • Housing data • Blocks in cities with populations of 50,000+ as measured by the previous census • 191 cities in 1940 • 1950 • 209 places in 1950

  5. Background • Enumeration Districts (EDs)–1870 to 1980 • 1960 • Total block population reported • 295 cities in 1950 • Additional 172 places paid for block level data • 1970 – first large scale enumeration using mail rather than door to door enumeration • Block coverage expanded to cover the expected extent of all 1970 urbanized areas • Contract block areas grew to 966

  6. Background • Enumeration Districts (EDs)–1870 to 1980 • 1980 • Blocks expanded to all incorporated places with a population of 10,000 or more • 5 states contracted for full state coverage of blocks (GA, MI, NY, RI, and VA) • Blocks covered 78% of the population and 7% of the land area

  7. Background • Current configuration of statistical geography -1990 to present • 1990 • TIGER (Topologically Integrated Geographic Encoding and Referencing System) database is developed • Nationwide block coverage established • Local census statistical areas committees participate in delineating block groups and tracts

  8. Background • Current configuration of statistical geography -1990 to present • 1990 (continued) • Redistricting Data Program introduces the block boundary suggestion project • Automated block creation and numbering introduced

  9. Background • Current configuration of statistical geography -1990 to present • 2010 • MAF/TIGER Accuracy improvement project performed prior to 2010 Census • Incorporated new features • Spatially realigned TIGER database to a higher level of precision

  10. Creation of tabulation blocks • Automated process – the “Tabulation Block Algorithm” • A series of criteria for formulating blocks (some of the considered criteria) • Geographic area boundaries • Feature type • Addressability of features • Block Boundary Suggestions • Previous census block boundary

  11. Creation of tabulation blocks • Geographic tabulation area boundaries are always held as block boundaries. • State & County boundaries • Incorporated Place • Minor civil division boundaries • Census designated place (CDPs) boundaries • Statistical areas (Census Tracts and Block Groups) • Certain Landmark boundaries (Military bases) • Et al.

  12. Creation of tabulation blocks • Certain features are also always held as block boundaries. • Roads classified as Primary Roads by MAF/TIGER Feature Classification Code (MTFCC) • Roads classified as Secondary Roads by MTFCC • Redistricting Data Program Block Boundary Suggestion Project “Must Holds” • Tribal Census Block Definition Program “Must Holds” (On tribal lands only)

  13. Creation of tabulation blocks • Other features can be used as block boundaries but are not always (examples) • Local Roads • Vehicular trails • Alleys • Railroads • Streams (Perennial Only) • Powerlines • National Park Boundaries

  14. Creation of tabulation blocks • Features can be classified as “Do Not Hold” • Unique to the Redistricting Data Program • Feature can not be classified as “Do Not Hold” if needed for a geographic tabulation area • All features and boundary types deemed as eligible to be a possible block boundary are given a priority value.

  15. Creation of tabulation blocks • All features deemed eligible are used to make a lattice of possible blocks • If a polygon’s boundaries are all required as block boundaries, it becomes a block • Remaining blocks are then evaluated for merging.

  16. Creation of tabulation blocks • Remaining block evaluations for merging • Minimum size • Iterative check accounting for size and bounding feature priority values • Single edge block • Addressable Feature • Bounding or internal • Isolated water block • Adjacent block qualifications

  17. Creation of tabulation blocks • Applying the block numbers • If the number of final blocks in a block group exceeds ~1000 then more merging occurs • Water blocks first • Lower priority edges • Block numbers assigned in a serpentine fashion starting in the northeast corner • First digit is block group number • Start at 000 and go until 999 or all block numbers have been assigned

  18. Creation of tabulation blocks • Where issues can arise • Feature attribution and classification • Connectivity of features in the feature network • Positional Accuracy

  19. Influencing Future Blocks • Participant Programs • Participant Statistical Areas Program (PSAP) • Boundary and Annexation Survey (BAS) • Redistricting Data Program (RDP) • School District Review Program (SDRP) • Initiatives • Geographic Support System Initiative (GSS)

  20. Influencing Future Blocks • Participant Statistical Areas Program • Tract and Block Group boundary definition • Define or modify Census Designated Places • Local Census Statistical Areas Committees or Census Regional Offices act as the participant • Pre-decennial program

  21. Influencing Future Blocks • Boundary and Annexation Survey (BAS) • Legal boundaries of incorporated places • Ongoing annual program • Partial and Full BAS years • Highest Elected Official is the invited participant

  22. Influencing Future Blocks • Redistricting Data Program • State Legislative and Congressional district boundaries – split blocks allowed • Voting Districts – new boundaries allowed • Block Boundary Suggestion Project • Non-partisan state liaison appointed by governor and legislature

  23. Influencing Future Blocks • School District Review Program • Elementary, Secondary, and Unified School District boundaries • Not as applicable to Florida due to county based school districts • State liaison

  24. Influencing Future Blocks • Geographic Support System Initiative • Focused on updating and maintaining the Master Address File • Includes components for updating and maintaining geographic features • Still in the research and design phase

  25. Key Points • Consistent participation in ongoing programs such as BAS • Coordination within states on state based programs • Participation in opportunities that arise from the GSS Initiative

  26. James Whitehorne Assistant Chief Redistricting Data Office U.S. Census Bureau www.census.gov/rdo rdo@census.gov 301-763-4039

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