Us Census Geographic Units for Indian Reservations

U.S. Census Geographic Units

Alex Samarin Why have standard geographic units?

• Valid comparison of data over time and across space – Over time: Comparing changes in same area from one survey to the next – Across space: Comparisons between defined geographic areas that change infrequently and in a traceable manner (e.g. census tracts being split or merged) Comparing geographic areas: Similarly named areas can differ in terms of the area they cover. Retrieving data and conducting analysis based on different geographic boundaries for will lead to different results.

http://www.sandag.org/uploads/publicationid/publicationid_874_3573.pdf Comparing geographic areas: Entities such as cities change boundaries in response to development and population growth that occur on a scale smaller than census tracts. New areas are annexed most often at the parcel level.

Shifting city boundaries are not stable enough for data collection or analysis.

http://www.sandag.org/uploads/publicationid/publicationid_874_3573.pdf Legal Geographic Units in CA

• State – County (58 statewide) – Incorporated Cities (18 in SD County) – American Indian Reservation or Rancheria (108 in CA, 18 in SD County) – California Senate (40) and State Assembly districts (80) – School Districts – Congressional Districts

• Legal Geographic units have legal boundaries that cannot change without legal steps – Electoral district boundaries change frequently Statistical Geographic Units in CA

• Statistical areas are created to identify an area for collection and tabulation of census data • Census Bureau Geographic Units – Block – Block Group – Census Tract – County • “Nested” Geographies – Boundaries do not cross – Data can be easily summed to next larger area

http://www.census.gov/geo/www/cengeoga.pdf Census Blocks • Stable, “atomic” level of Census geography – Smallest geographic area at which the Census Bureau publishes decennial (100% sample, not ACS) data – No more than 97 blocks per block group – Basis for all other data tabulations, nest within all other Census geographic units – Bounded by streets, stream, property lines, other district boundaries (e.g. school districts) • Urban areas Æ often defined as a city block bounded by streets • Suburban areas Æ larger, irregular areas defined by a variety of features • Remote areas Æ can be hundreds of square miles

http://www.census.gov/geo/reference/pdfs/GARM/Ch11GARM.pdf Block Group

• Contiguous clusters of blocks within same census tract – Smallest geographic area at which the Census Bureau publishes sample data (Sample size < 100%) • Population: 600 – 3,000 – Average 1,500 – Share boundaries with encompassed blocks Census Tracts • Small, relatively permanent statistical subdivisions of a county (nest within county boundaries) • Size depends on population density – Share boundaries with blocks and block groups • Average population ~ 4,000 – 1,200 minimum – 8,000 maximum

http://www.census.gov/geo/education/pdfs/CensusTracts.pdf Census Tract 2000‐2010 Boundary Changes Census Tract Changes • Split census tracks – Tracts are split when population in a tract exceeds 8,000 – Common occurrence in San Diego County

• Merged census tracks – Tracks are merged when population in a tract is less than 1,200 – Ensures a representative sample for data collection and tabulation – Seen for first time in San Diego County with 2010 Census

• Boundary adjustment – Adjusted to better follow physical features or other district boundaries, or to make minor population changes that don’t warrant a merge or split http://www.census.gov/geo/education/pdfs/CensusTracts.pdf http://www.sandag.org/resources/demographics_and_other_data/demographics/census/data.asp Dealing with census tract boundary changes Comparing Census data in split tracts to earlier years: ‐ Add up data from new tracts, compare to original, larger tract from previous census

Identifying merged tracts: In San Diego County, merged census tracts are identified with a code of 214 or greater. Tracts codes from 2000 and earlier that were merged in 2010 do not occur in 2010 Census.

Comparing 2010 Census in merged tracts to earlier years: ‐ Add up data from previous, smaller tracts to compare to new, larger tract in 2010 Census Census Geographic Units for Indian Reservations

http://www.census.gov/geo/www/aianahhb.pdf Identify Census Geographic Units

• American FactFinder

http://factfinder2.census.gov/faces/nav/jsf/pages/searchresults.xhtml?refresh=t Sources

SANDAG INFO, September 2002, No. 3. Geographic Area Help Define the San Diego Region. http://www.sandag.org/uploads/publicationid/publicationid_874_3573.pdf

United States Census Bureau. 2010 Geographic Terms and Concepts. http://www.census.gov/geo/reference/terms.html#

United States Census Bureau. Census Tracts. http://www.census.gov/geo/education/pdfs/CensusTracts.pdf