Resources for Decennial Censuses
Before 1970
1970
1980
1990
2000
Resources for Comparing Censuses
1970, 1980, 1990 and 2000
1980 to 2000
1990 to 2000
Amanda C. Henley
GIS Librarian
Davis Library
Census Geography is the term used to describe the areas for which the U.S. Census Bureau tabulates variables. These areas are updated for each census.
Examples include: counties, tracts, block groups, and blocks.
Blocks are the smallest census geography. Only general population characteristics are provided at the census block level. Block level data comes from the short form questionnaire, which everyone receives.
More detailed population characteristics are obtained from the long form, which is given out to a sample (one in six households). These detailed data are available down to the blockgroup.
Boundaries change between censuses. The boundaries of many census geographic units are based on population. Therefore, the boundaries of these units change with population density. There are some options for those who wish to normalize data spatially so that comparisons can be made in spite of changing boundaries. Contact GIS Services for more information.
The nation was not broken down into tracts, block groups, and blocks for all censuses. For example, there are many portions of North Carolina that were not broken down into tracts in 1980. Before attempting to make a comparison between censuses for a certain level of geography, verify that the area of interest was indeed divided into that level of geography for the census years being compared.
Some of the questions asked on the census questionnaire have changed over time. The ways in which respondents have been instructed to answer census questions have also changed. For example, race data from the 1990 census is not directly comparable to race data from the 2000 census. This is because in 1990, respondents had to choose one race; in 2000, respondents could choose all that were applicable. In order to make a valid comparison between two censuses, ensure that the questions asked during the two censuses were identical and that the questions were answered in an identical way.
For detailed information about the census questionnaires and instructions, see: "Measuring America: the decennial census from 1790 to 2000" (U.S. Census Bureau, 2002). For information about the types of data available on the censuses at a glance, see "Population and Housing Items on the General Census Schedules 1970-2000", a table compiled by Grace York, University of Michigan Library.
