Census Geography

Montana SDC Affiliate meeting

HelenaNovember 6, 2013

Geospatial Foundation at Census

•Topologically•Integrated•Geographic•Encoding•Referencing

TIGER

Classes of Census Geography• Political Geography:

– States, Counties, Cities, American Indian Reservations, Minor Civil Divisions, etc…

– These boundaries may change between censuses• Statistical Geography:

– Census Tracts, Census Blocks, Voter Districts, Traffic Analysis Zones, etc…

– Designed to display Census data for research and analysis in the public and private sector and most do not change between censuses

• County• Census Tract

– Relatively homogeneous population characteristics

– Population ~ 1200-8000 • Block Group

– Lowest level for ACS data

• Block– Bounded on all sides by

visible and nonvisible features

– A city block in urban areas

Geographic Hierarchy

State

County

Tract

Tract

Block Group

Block

Block

History of the Census Tract

13

1790 First census

1890 First delineation of small geographic areas called sanitary districts

1906

1910

Dr. Walter Laidlaw suggested the delineation of permanent, small geographic areas that would retain their boundary census to census

Dr. Laidlaw divided NYC into “districts” and asked Census to do the same for seven other cities

1920 Dr. Laidlaw published data by district for NYC

1930 Howard Wipple became chairman of the Committee on Census Enumeration Areas and promoted the use of census tracts

History of the Census Tract

14

1940 The census tract became an official geographic entity for which the Census Bureau would publish data. Census tracts covered major cities and block number areas (BNAs) covered many other cities

1980 The number of BNAs increased and the criteria of the BNA matched the census tract

Census tracts or BNAs covered the entire nation (and so do blocks)1990

2000 The BNA concept was retired and census tracts were defined nationwide.

100th anniversary of the census tract!!2010

Where can you get TIGER data?

www.census.gov/geo

Sources of Census Geography• TIGER/Line® Shapefiles

– http://www.census.gov/geo/www/tiger/• Download files by county• Get all levels of geography available for a county or state

• TIGERweb–http://tigerweb.geo.census.gov/tigerwebmain/TIGERweb_main.html

• Interactive and WMS access to roads, streams and various boundaries that are found in TIGER data.

• Shapefiles with Demographic Data• Select Geographic areas with SF1 data pre-joined• Shapefiles or Geodatabases

What About Updates?

• How does the Census Bureau keep the geography current?

Some Geographic Participant Programs

• Boundary and Annexation Survey (BAS)– Updates all legal boundaries and names– Boundaries used to tabulate data in:

• American Community Survey, Decennial Census, Population Estimates Program

• Redistricting Data Program– Public Law 94-171

• Participant Statistical Areas Program(PSAP)

Public Law 94-171

• Enacted in 1975, directs the U.S. Census Bureau to provide redistricting data needed by the 50 states.

• Specifies that within a year following Census Day (by April 1), the Census Bureau must send the governor and legislature in each state the data they need to redraw districts for the United States Congress and state legislature.

Statistical Areas Program

• Involves local governments• Conducted once each decade• Includes;

– Tracts– Block Groups– Census Designated Places (CDP)

Summary

• TIGER® holds all Census Geography– The public can access the data through

TIGER/Line® or via TIGERWeb

• Each piece of geography has a unique identifier that is needed to link it to the demographic data

The End!