Massachusetts Institute of Technology Department of Urban Studies and Planning 11 520 A Workshop on Geographic Information Systems 11 188 Urban Planning and Social Science Laboratory Making Sense of the Census October 12 2005 Overview What is it and why do we care How the data are collected What data are available Introduction to Census geography and summary levels A Quick Look at the Census documentation A Quick Look at some sample data What Is It and Why Do We Care Mandated by the Constitution of the United States The modern census of population and housing was established in 1940 with the incorporation of the housing component and the introduction of sampling techniques for the long form Conducted every ten years Attempts an actual count of population categorized by various criteria The only source for demographic data with a wide geographic scope The most reliable and detailed information for describing local areas neighborhoods cities counties The most consistent source of time series demographic data available U S Congressional representatives are apportioned based on census counts Federal dollars for schools employment services highway assistance housing construction hospital services programs for the elderly etc are all distributed based on census figures How the Data Are Collected Collected from households through a mail survey conducted every decade For the 2000 Census more than 285 000 census takers and support personnel accounted for the 118 million households and 275 million persons in the United States o 2000 Census Home Page Two different census questionnaires are distributed o short form questionnaire contains questions asked of everyone summarized in Summary Tape File 1 STF 1 for 1980 and 1990 Summary File SF 1 for 2000 o long form questionnaire contains questions asked of a population sample 1 6 households summarized in Summary Tape File 3 STF 3 for 1980 and 1990 Summary File 3 SF 3 for 2000 The long form is being replaced in the 2010 Census by the American Community Survey This program will survey homes every month and provide updated statistics every year instead of every ten years The program begins in 2003 What s Included Information on Population Employment and Housing Characteristics Short Form 100 Count STF 1 SF 1 Population Characteristics Housing Characteristics Age Tenure Gender Value or Contract Rent Race Vacancy Status Hispanic Origin Number of Rooms Marital Status Units in Structure Household Type Congregate Housing Household Relationship Sample Short Form from 2000 Census Long Form Sample Counts STF 3 SF 3 Population Characteristics Housing Characteristics Social Characteristics Age of Housing Education Heating Fuel Citizenship Facilities Ancestry Vehicles Language Mortgage Status Disability Children Place of Birth Economic Characteristics Income Labor Force Status Employment Place of Work Public Assistance Retirement Income Sample Long Form from 2000 Census Why We Need to Know the Two Components Accuracy of the data varies and counts differ Why It helps us to understand how the data are organized in Summary Tape Files STFs Census Geography and Summary Levels The Census organizes and aggregates data into a series of geographic hierarchies Overview Standard Hierarchy of Census Geographic Entities from Census 2000 Summary File 1 Technical Documentation prepared by the U S Census Bureau 2001 p A 25 Summary Geographic Unit Level 010 United States 020 Region Northeast NE Midwest MW South S and West W Regions 030 Division Northeast New England Mid Atlantic Midwest East North Central West North Central South South Atlantic East South Central West South Central West Mountain Pacific State includes Washington D C Puerto Rico 040 050 County 060 County Subdivision 070 Place Census Tract Block Numbering Area average 4 000 persons 080 090 Block Group average 1 000 persons 100 Block average 85 persons State County Tract Block Group Nesting Summary Level Geographic Unit 040 State includes Washington D C Puerto Rico 050 County 140 Census Tract 150 Block Group Supplemental Geographic Areas Summary Level Geographic Unit 400 Urbanized Areas 300 Metropolitan Areas MSAs CMSAs 200 American Indian and Alaska Native areas 800 ZIP codes Hierarchy of American Indian Alaska Native and Native Hawaiian Entities from Census 2000 Summary File 1 Technical Documentation prepared by the U S Census Bureau 2001 p A 26 A Visual Look at Census Geography o Continental United States Regions in blue Divisions in green States in brown o Counties o A Closer Look at Southern New England Counties o Tracts black lines and Block Groups green lines in Suffolk County MA Census Geography Concepts o The census block is the basic level o Confidentiality must be maintained and data about individual persons and households are not revealed o More detailed data are provided for higher levels of geography Why o Many but not all items are available at multiple summary levels Potential Problems o The same geographic name is used for summary levels corresponding to different aggregations o Geographic areas at lower levels may be subdivided by higher levels of geographic units E g a census tract may be split by town boundaries o The same variable names are used for different variables in the STF SF 1 and STF SF 3 o The way variable values are encoded makes identifying the meaning of variables difficult o ZIP codes do not overlay other units cleanly o Geographic boundaries change with time making time series analysis difficult Obtaining Census Geographic Boundary Files for Use in a GIS ArcView shapefiles and ArcInfo coverage formats are readily available for 1990 and 2000 Census geography boundaries Boundary files from the U S Census Bureau Redistricting TIGER 2000 from ESRI s Geography Network Census Summary Files The most useful files distributed by the Census Bureau are the Summary Tape Files now renamed simply Summary Files that aggregate the individual census forms to various levels of census geography The Census Bureau distributed the 1990 Census files as DBF files on CD ROMs In what looks like a recent development the Census Bureau has posted the contents of many 1990 CD ROMs online These are available via HTTP and FTP An online forms based interface called 1990 Census Lookup is available Now American FactFinder provides another forms based online interface In fact the 1980 STF 1 and STF 3 are now online You can obtain the 1980 STF 1 via HTTP or FTP and the 1980 STF 3 via HTTP or FTP Documentation is