Understanding Census Geography

Lisa Neidert

NPC Workshop: Analyzing Poverty and Socioeconomic Trends Using the American Community Survey

July 12 – July 15, 2010

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/Products/users_guide/acs_2008_reference_maps.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 2006-2006 ACS

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

Geographical Areas (Texas):Covered in 2006-2008

ACS 2006=2008 Geographical Areas

What’s available in the ACS: via Look-up tables

Geographic entities available for 1-year data (2008)

Geographic entities available for 3-year data (2006-2008)

Not ready for prime-time:census tracts and zip codes

Need 5-year estimates file 2005 – 2009 Available 2010 for Census Tracts; 2011 for Zip Codes

Annual updates thereafter 2006 – 2010 2007 – 2011, etc.

Possible delay for 5-year data – only an unsubstantiated rumor

ExampleCensus Tracts for community districts

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.html Fun resource

http://en.wikipedia.org/wiki/Zip_code

What to do with a 2011 release of zip code data?

See Exercise 4: http://www.psc.isr.umich.edu/dis/workshop/npc2010/

Exercise4_DealingWithDelays.pdf

This exercise shows how to build zip code characteristics from census tract characteristics

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 dataUnit is county

Statistics based on 1-year ACS dataUnit is PUMA

Illinois example:PUMA to county example

PUMA to County Widget

Based on PDQ-Explore output http://www.psc.isr.umich.edu/dis/data/resource/detail/1527

Based on American FactFinder output http://www.psc.isr.umich.edu/dis/data/resource/detail/1528

Try one this week

Class Exercises Today

http://mblog.lib.umich.edu/NPC2010/archives/class_exercises/index.html

Poverty Hot-spots (ACS 2008) Census tract data (Census 2000) Bulk downloads, zip code (Census 2000) Dealing with Delays: Creating zip code characteristics from

census tract data

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 http://www.psc.isr.umich.edu/dis/data/ref/PUMA

/SUPERPUMA-2000-5pct.html

Metropolitan areas

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

es/metrodef.html

Historical Definitions http://www.census.gov/population/www/estimat

es/pastmetro.html

Researcher is free to follow own definitions Census Bureau follows OMB definitions