American Community Survey FAQ

The Premium ACS version of our Microsoft Excel add-in, CDXZipStream, contains five data feeds sourced from the U.S. Census Bureau’s American Community Survey.  The data covers a range of geographies including state, county, city, and ZIP Code (or ZCTA).  A separate feed is also available for census tracts.

Here’ a roundup of questions we often receive about the ACS:

What is the American Community Survey?  The ACS is a survey that has been performed by the U.S. Census Bureau every year since 2005; it has replaced the old "long form" that used to be part of the decennial (10-year) census.  Starting in 2010, the decennial census now only consists of the "short form" that covers basic questions about age, gender, race, and household size.  The more interesting demographic data such as income, educational attainment, and other socioeconomic factors are now being obtained exclusively through the ACS.

Why can't all feeds use data from the latest available year?  The American Community Survey only surveys a portion of the U.S. population every year (about 3 million households) and one year does not provide enough data to provide a statistically significant result for the smaller geographies. Data for ZCTA's for example, are only provided over a five-year range, where all data are combined over this time period.

What is the difference between a ZIP Code and ZCTA?  ZIP Code areas are defined by the US Postal Service to facilitate mail delivery, and do not align with any census geography.  ZIP Codes are approximated by combining data from smaller US Census Bureau-defined blocks into areas called ZCTAs (ZIP Code Tabulation Areas).  They are generally a very good, but not perfect, match.

Why isn't my ZIP Code listed?  In creating ZCTAs, the Census Bureau uses the most frequently occurring ZIP Code for the addresses in each census block. If a ZIP Code covers only a few addresses, and is not the most frequently occurring ZIP Code in a block, it will not be assigned a ZCTA.  Also, in most cases PO Box Only ZIP Codes are not assigned ZCTAs.

Why is there no population shown for my ZIP Code?  ZCTA's can includes both residential and commercial addresses.  Commercial areas, or unique areas such as college campuses, may not have a household population.

Why don't all the population fields add up to the total population?  The Census Bureau considers Hispanics to form an ethnicity, rather than a race, and do not include them as part of the race population data. Adding Hispanic and non-Hispanic population fields, however, will match the total population.

Why isn't my town (or place) listed?  The CDXACSPlace data feed covers towns, cities, boroughs etc. for populations of 20,000 or more. Although the Census Bureau does provide data for about 30,000 places, we have not included them all in order to keep the ACS database to an easily downloadable size.

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