Note on two types of ZIP codes: There are two types of ZIP Code reported on IECAM: postal ZIP code and census ZIP code or ZCTA.
- Postal ZIP code. This ZIP Code, used by the U.S. Postal Service, is what people generally think of when they think of ZIP codes. However, the postal ZIP code is a delivery route. It is NOT a geographic area (although it sometimes approximates a geographic area). Its purpose is to foster more efficient mail delivery. There are many parts of the US that do not have ZIP codes because they are not on postal delivery routes. Note that ZIP codes change every year as new ZIP codes are created and old ZIP codes are eliminated, combined, or split.
- Census ZIP code, or ZIP Code Tabulation Area (ZCTA) This ZIP code is used by the U.S. Census Bureau. It is an artificial area created by the Census Bureau using Census Blocks. The ZCTA is very roughly similar to the geographic area of a corresponding postal ZIP code (for only those postal ZIP codes that approximate geographic areas).
ZIP (Zone Improvement Plan) Code is a system of 5-digit codes, established in 1963, that identifies the individual post office or metropolitan area delivery station associated with an address. The first three digits identify the delivery area of a sectional center facility or a major-city post office serving the delivery address area. The next two digits identify the delivery area of an associate post office, post office branch, or post office station.
ZIP+4 is a nine-digit numeric code, established in 1981, that is composed of: (a) the initial five-digit code (see above) and (b) the four-digit expanded code: the first two additional digits designate the sector (a geographic area) and the last two digits designate the segment (a building, floor, etc).
Source of definition: U.S. Postal Service ZIP Code FAQs
Note on yearly changes in ZIP Codes Postal: Postal Zip codes change every year as new ZIP codes are created and old ZIP codes are eliminated, combined, or split.
Presentation of early care and education data by Zip Codes Postal: IECAM presents data by ZIP Codes Postal for all years for the number and capacity of early care and education sites (PFA, Head Start, child care). These data are user-reported. IECAM has found, in the data that it receives on early care and education services, that there are many errors in user-reported postal zip codes. IECAM makes an effort to correct obvious errors, but cannot guarantee that all postal ZIP codes are accurate.
Note on presentation of demographic data by Zip Code Postal: Because the Census Bureau does not estimate data by postal zip codes (because they are not geographic areas), IECAM cannot present demographic data by Zip Codes Postal.
Note on comparing data by “ZIP Codes Postal” across years: Comparing early care and education service data (i.e., number of sites or capacity of PFA, Head Start, child care) for postal ZIP codes across years is possible. However, note that there are two serious concerns with such comparison. First, because postal ZIP codes change every year, no two years’ ZIP code lists are the same. Second, because the postal ZIP codes are user-reported and because it’s not possible to correct all user-reported errors, IECAM does not guarantee that all user-reported postal ZIP codes are correct.
Note on ZIP Code Tabulation Areas (ZCTAs) are approximate area representations of U.S. Postal Service (USPS) five-digit ZIP Code service areas that the Census Bureau creates using whole census blocks to present statistical data from censuses and surveys. The Census Bureau defines ZCTAs by allocating each block that contains addresses to a single ZCTA, usually to the ZCTA that reflects the most frequently occurring ZIP Code for the addresses within that tabulation block.
Source of definition: U.S. Census Bureau, Geography Division. Geographic Terms and Concepts – ZIP Code Tabulation Areas (For an explanation of census blocks, see Geographic Terms and Concepts – Block)
Note on two iterations of ZCTAs: There was a ZCTA iteration created in 2000 and another in 2010.
- 2000 ZCTAs. This is a ZCTA delineation by the U.S. Census Bureau that was created in 2000. This series was used in reporting census data beginning in 2000 and continuing through 2009. Note that, because postal ZIP codes change every year while ZCTAs do not, there is a lack of correspondence between the two that increased from 2000 through 2009. Postal ZIP codes may exist for which there are no ZCTAs, and ZCTAs may exist for which a postal ZIP code has been eliminated.
- 2010 ZCTAs. This is a ZCTA delineation by the U.S. Census Bureau that was created in 2010. This series was used for reporting census data beginning in 2010 and will continue to be used in the foreseeable future. The Census Bureau notes that there are significant changes in the 2010 ZCTA delineation compared to the 2000 ZCTA delineation. Note that, because postal ZIP codes change every year while ZCTAs do not, there is a lack of correspondence between the two that will increase the farther we get from 2010. Postal ZIP codes may exist for which there are no ZCTAs, and ZCTAs may exist for which a postal ZIP code has been eliminated.
Note on the presentation of data by ZIP Codes ZCTA 2000: IECAM does not present data by ZCTA 2000 for years 2009 and earlier.
Note on the presentation of data by ZIP Codes ZCTA 2010: IECAM presents early care and education data and demographic data by ZIP Codes ZCTA 2010 for years 2010 and later.
Note on comparing data by “ZIP Codes ZCTA 2010” across years: Because there are no changes to the ZCTA 2010 areas across years, it is appropriate to compare data on early care and education services, as well as demographic data, across years.
Note on comparing data between “ZIP Codes Postal” and “ZIP Codes ZCTA 2010”: Given that the postal ZIP code is a delivery route and the ZCTA is a geographic area that artificially tries to approximate the postal ZIP code, these two ZIP code types are not precisely comparable. For example, a child care center with a postal ZIP code of 618xx may not be located in the ZCTA 618xx.
Given that Postal ZIP Codes change every year and that ZCTAs do not, there might be Postal ZIP Codes that have no corresponding ZCTA, and vice versa.
For these reasons, IECAM does not recommend comparing early care and education service data (i.e., number of sites or capacity of PFA, HS, child care) by ZIP Codes Postal with ZIP Codes ZCTA 2010.