Source: U.S. Census Bureau
Release Date: October 1997
Revised: May 2006
The Census Bureau's population estimates are produced using annually updated decennial census base population counts. These updated counts are referred to as the "population estimates base" to distinguish them from previously published census population totals. The population estimates base reflects corrections, boundary changes, and other geographic updates since the last census. The geographic change notes describe the most significant of these changes and are intended to assist data users working with population estimates time series data.
The post-2000 population estimates reflect legal boundary changes reported nationwide via the annual Boundary and Annexation Survey (BAS). In that survey, governmental units are asked to report the boundaries legally in effect as of January 1 of the current calendar year. Geographic changes collected via the BAS are incorporated annually into the estimates base, using an automated processing system termed the Geographic Update System to Support Intercensal Estimates (GUSSIE). Generally, all BAS changes submitted to the Census Bureau by April 1 of the calendar year will be reflected in the population estimates for that year.
In general, increases or decreases in land area are accompanied by corresponding changes in the base population of each governmental unit. When governmental units are merged, their respective base populations are combined. Base populations are calculated for new governmental units, and base populations of incorporated places or townships that dissolve become part of the unincorporated balances of the counties in which these governmental units are located. In other instances, base population increases or decreases in areas with few or insignificant boundary changes may reflect improvements in the geographic assignment capabilities of the Census Bureau’s TIGER® System and associated Master Address File.
The notes are organized by state and currently include the following types of changes:
The following statistical areas are included in population estimates products:
The Census Bureau is enacting post-Census 2000 programs, many in conjunction with local governments, to further improve the geographic information in the TIGER® System with direct benefits for the Population Estimates Program and the American Community Survey. This information will include census corrections and geographic boundary updates that occurred after Census 2000. The July 1, 2005 county and subcounty population estimates reflect boundary updating current to January 1, 2005 and Count Question Resolution corrections processed through September 30, 2003.
Corrections to population counts resulting from the Census 2000 Count Question Resolution Program are not included in the notes, but are available for review and downloading on the Census Bureau’s Web site, at: http://www.census.gov/prod/cen2000/notes/errata.pdf.
Historical documentation about corrections resulting from the Census Bureau’s 1990 Count Question Resolution program is not on the Web site, but is available in a Census Bureau report, Corrected 1990 Census Population, Housing Units, and Group Quarters Counts for Governmental Units (CPH-L-157).
Estimates geography boundary files for use in a geographic information system (GIS) or other mapping software are available for download. See http://www.census.gov/geo/www/cob/.
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