The following changes to Census geography have been made, in an effort to make the 2000 Census data more useful to the public:
Change From Block Numbering Areas (BNAs) to Tracts.
A census tract is a statistical area that was created to provide data for
small areas, like neighborhoods. For 1990 the BNAs were a companion level of
geography with the census tract. The only real difference was that, unlike
tracts, there was no local involvement in their creation. That is, state agencies or
the Census Bureau delineated them. From the user's perspective there was no practical
difference between census tracts and BNAs.
For Census 2000, the separate BNA and census tract programs have been consolidated into one program of census tracts. Therefore, there will be no BNAs in Census 2000 geography.
Census Designated Places (CDPs).
A CDP is a statistical area that represents a locally known concentration of
population that is identifiable by name but that is not legally incorporated
and therefore has no official boundaries. However, State and county governments often want
census data for these areas. The Census Bureau works with localities that are interested in
such a program before each census to determine boundaries for these areas. These
communities have to meet the CDP criteria,
such as having a mix of commercial and
residential activities and being locally recognized place. Creating CDPs enables named localities
to become geographic entities, for which statistics can be published.
In the 1990 Census, such areas had to have a minimum population to be recognized as a CDP. We have eliminated the minimum population requirements for Census 2000. This will enable smaller communities, typically in rural areas, to qualify for statistical data tabulation.
Census Block Number.
The Census block is the smallest area for which the Census Bureau publishes
statistics. Each census tract is divided up into many blocks.
For Census 2000, block numbers have 4 digits. Also, the creation and numbering of the census blocks was done much later in the Census cycle; well after the reference date for Census 2000 legal boundaries: January 1, 2000. In 1990 we were not able to create all of the blocks possible in some areas because we did not have a sufficient number of code numbers available.
For the 1990 Census, the block boundaries were delineated well before the boundary reference date of January 1, 1990. Because some boundaries changed between the block delineation and the boundary reference date, the Census Bureau had to add suffixes to portions of the affected blocks. By waiting to delineate the census blocks, the Census Bureau did not need to add a suffix to accommodate boundary changes just before the Census reference date. The 4-digit block number enabled the creation of more blocks.
ZCTA (ZIP Code Tabulation Area).
New for Census 2000 is the ZIP Code Tabulation Area. This is a new statistical area that
the Census Bureau has created to address the problems associated
with tabulating data by ZIP Codes. ZCTAs are generalized representations
of U.S. Postal Service (USPS) ZIP Code areas. ZIP Codes are mail delivery
routes, created by the USPS as a tool to help facilitate the
delivery of mail and were never intended to provide the basis
for statistical tabulations. Therefore, they are often not appropriate for that use.
ZIP Codes are usually just collections of streets that represent postal
carrier routes and were not created to be a polygon with predefined boundaries. To further
complicate matters, ZIP Codes can be assigned to just one
building or even to a single company within a building and can be changed to meet
operational needs of the USPS. To be able to provide statistical data by ZIP Code, the Census Bureau
created the ZCTA: a close approximation of an actual ZIP Code coverage. Unlike ZIP
Codes, ZCTAs have the characteristics of other statistical areas, such as definable
boundaries, making it possible to use ZCTAs in statistical tabulations.
The Census Bureau refers to the addresses in its TIGER and Master Address File databases to determine the areas covered by each ZIP Code; the Census Bureau then uses that information to interpolate boundaries for these areas as they relate to Census 2000 blocks. This means that the Census Bureau will create ZCTAs by grouping whole Census blocks. The ZIP Code used by the majority of addresses in a given block will be the ZCTA code for that block. While there is no legal or operational requirement for the USPS to abide by these boundaries, the Census Bureau believes that ZCTAs will closely follow actual ZIP Code coverage in practice. The Census Bureau intends to update ZCTA boundaries periodically, as resources permit, to incorporate changes in ZIP Codes. For more information on ZCTAs visit this URL: http://www.census.gov/geo/ZCTA/zcta.html .
The new standards for defining Metropolitan and Micropolitan Statistical Areas are outlined in the
Office of Management and Budget's Federal Register / Vol. 65, No. 249 / (Wednesday, December 27, 2000 ), URL:
http://www.census.gov/population/www/estimates/notice001227.pdf
For specific information, refer to the Census Bureau's Metropolitan Area
Standards Review Project web page, URL:
http://www.census.gov/population/www/estimates/masrp.html
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Source: U.S. Census Bureau
