Understanding Census Geography

Lisa Neidert McCormick Specialized Training Institute October 28 – October 30, 2009

Census Geography

Geographic Areas:

with 1-year and 3-year data

Geographic Areas:

with 1-year and 3-year data

What’s available in the ACS for single year data: via maps  Maps showing counties and places for each state (or the nation)  http://www.census.gov/acs/www/Product s/users_guide/acs_2008_reference_map s.htm

Counties with single year data:

ACS 2008

Almost all counties: DE, MA

Few counties, no places: VT and WY

State with American Indian Places: AK, AL, LA, NC, OK

Counties with 3-year data:

ACS 2006-2008

States where all counties are over 20,000

 Connecticut  Delaware  District of Columbia  New Hampshire  New Jersey  Rhode Island

What geographies are available in the 2006-2008 ACS?

http://www.census.gov/acs/www/acs-php/2006_2008_beginner_users_guide.php

What’s available in the ACS: via Look-up tables  Geographic entities available for 1-year data (2007)  Geographic entities available for 3-year data (2005-2007)

Not ready for prime-time: census tracts and zip codes  Need 5-year estimates file  2005 – 2009  Available 2010  Annual updates thereafter   2006 – 2010 2007 – 2011, etc.

Example

Census Tracts for community districts

Community District 11: Manhattan, East Harlem

Zip codes  Not census geography  However, big demand for zip code data  Census Bureau builds ZCTAs via census blocks  ZCTA FAQs  http://www.census.gov/geo/ZCTA/zctafaq.h

tml  Fun resource  http://en.wikipedia.org/wiki/Zip_code

What are PUMAs?

 Public Use Microdata areas  Combination of population geographies that sum to at least 100,000 population.

 In rural areas, several counties will form a PUMA. In an urban area, a county will be subdivided into multiple PUMAs.

 PUMAs do not cross state boundaries

PUMAs. . . .

 PUMAs do not have good comparability over time (1990, 2000).

 PUMA geographies for the ACS are the same as the 2000 boundaries  PUMAs are reasonable substitutes for counties  Smallest geography available in the microdata.

PUMAs. . .  Can be valuable for bypassing geographic restrictions when one wants national information at the county level  Create pseudo counties based on a cross-walk between PUMAs and counties

Statistics based on 1-year ACS data Unit is county

Statistics based on 3-year ACS data Unit is county

Statistics based on 1-year ACS data Unit is PUMA

Illinois example: PUMA to county example

PUMAs via Maps  Reasonable tool for rural parts of a state  Somewhat unwieldy for urban areas  Multiple maps per state http://usa.ipums.org/usa/volii/2000pumas.shtml

PUMAs via text  Describes PUMA composition  By:  County  County subdivision  Place  Census tract  http://usa.ipums.org/usa/volii/2000pumas.shtml

Metropolitan areas

  Defined by Office Management Budget (OMB) http://www.census.gov/population/www/estimat es/metrodef.html

 Frey, et. al. “Field Guide”  http://www.psc.isr.umich.edu/dis/census/brookin gs.pdf

  Users are free to follow own definitions Census Bureau follows OMB definitions