ZIP Code® Tabulation Areas (ZCTAsTM)
ZIP Code Tabulation Areas (ZCTAsTM) are a statistical entity developed by the U.S. Census Bureau for tabulating summary statistics from Census 2000. This concept was developed to overcome the difficulties in precisely defining the land area covered by each ZIP Code®. Defining the extent of an area is necessary in order to accurately tabulate census data for that area.
ZCTAs are generalized area representations of U.S. Postal Service (USPS) ZIP Code service areas. Simply put, each one is built by aggregating the Census 2000 blocks, whose addresses use a given ZIP Code, into a ZCTA which gets that ZIP Code assigned as its ZCTA code. They represent the majority USPS five-digit ZIP Code found in a given area. For those areas where it is difficult to determine the prevailing five-digit ZIP Code, the higher-level three-digit ZIP Code is used for the ZCTA code.
ZIP Code Information
The Census Bureau does not have maps or digital files showing the boundaries of U.S. Postal Service ZIP Codes. The fact that ZIP Codes aren't required to be polygons makes them difficult to map. They are networks of streets served by mail carriers or just individual post offices and are a tool for mail delivery. They also change periodically as required to meet Post Office operational needs. Various companies have created maps by interpolating boundaries between occurrences of ZIP Codes on the ground. However, this does not guarantee that the U.S. Postal Service delivery routes will follow this interpretation.
In the past, the Census Bureau produced the 1990 Gazetteer ZIP Code file and a 1999 ZIP Code file. These files were byproducts of Census Bureau internal operations. They were not developed as a formal product. However, the Census Bureau has made them available to the public "as is." There will be no updated versions of these files.
The Census Bureau did not produce data files containing U.S. Postal Service ZIP Codes either as part of the Census 2000 product series or as a post Census 2000 product. However, due to the public's interest in having statistics tabulated by ZIP Code, the Census Bureau has created a new statistical area called the ZIP Code Tabulation Area (ZCTA) for Census 2000. The ZCTAs were designed to overcome the operational difficulties of creating a well-defined ZIP Code area by using Census blocks (and the addresses found in them) as the basis for the ZCTAs.
There is no correlation between U.S. Postal Service ZIP Codes and U.S. Census Bureau geography. This is because individual U.S. Postal Service ZIP Codes can cross state, place, county, census tract, block group and census block boundaries (just to name a few). The geographic entities the Census Bureau uses to tabulate data by are relatively stable over time. For instance, census tracts are only defined every ten years. In contrast, U.S. Postal Service ZIP Codes are designed to meet the day-to-day operational needs of the U.S. Postal Service and tend to change more frequently than every ten years. Because of the ill-defined nature of ZIP Code boundaries, the Census Bureau does not have a file (crosswalk) showing the relationship between U.S. Census Bureau geography and U.S. Postal Service ZIP Codes.
ZIP Codes and Metropolitan Statistical Areas. The Census Bureau does not have any file that will relate Metropolitan Statistical Areas to U.S. Postal Service ZIP Codes.
ZIP Code Corrections. The Census Bureau cannot make ZIP Code corrections to its data sets based on e-mail messages. They can use only information that they receive through their cooperative operations with the U.S. Postal Service.
Further, the Census Bureau does not offer "crosswalk" or "relationship" files that associate U.S. Postal Service ZIP Codes to any legal and statistical census geography. For the most accurate and up-to-date ZIP Code data, we suggest contacting the source for ZIP Code information: the United States Postal Service. For the most definitive information on U.S. Postal Service ZIP Codes, contact the U.S. Postal Service.
1. How do you pronounce ZCTA?
The acronym ZCTA is pronounced zik'tah.
2. What Census 2000 products incorporate ZCTAs?
- Census 2000 TIGER/Line® Files:
ZCTAs for the entire United States and Puerto Rico are available in the Census 2000 TIGER/Line® files. ZCTAs are stored in Record Type S, which stores codes that relate to TIGER polygons.
- American FactFinder Internet site:
Users can plot ZCTA maps and create tables showing census data tabulated by ZCTAs
- Cartographic Boundary Files:
Generalized boundary files, including ZCTAs, that are appropriate for small-scale thematic mapping. These files are available for downloading from the Census Bureau's Cartographic Boundary Files site in the following formats: ARC/INFO Export (.e00), Arcview Shape (.shp), and ASCII.
LandView is a desktop mapping system that includes database extracts from the Environmental Protection Agency, the U.S. Census Bureau, and the US Geological Survey. These databases contain ZCTA boundaries along with jurisdictional boundaries, roads, rivers, and railroads, census block groups and census tract polygons, schools, hospitals, churches, cemeteries, airports, dams, and other landmark features. LandView is available on DVD (Digital Versatile Disc) data disks with geographic files for the entire country (all 50 states, the District of Columbia, and Puerto Rico). The software will run on both Windows and Macintosh computers.
- Summary Files 1 through 3 (SF1 – SF3):
Population and housing characteristics from Census 2000. Data are tabulated by ZCTA. SF1 and SF2 are the 100-percent data from the Census 2000 short form, and SF3 is sample data from the long form.
3. Do ZCTAs cover the entire United States?
ZCTAs cover all 50 states, the District of Columbia and Puerto Rico.
4. How many ZCTAs cover the nation?
There are 33,178 ZCTAs nationwide (all 50 states, the District of Columbia and Puerto Rico), including generic three-digit ZCTAs. Of that total, 32,038 ZCTAs carry the full five-digit numeric ZIP Code. The remainder will have a generic code ending in either “HH” or “XX” suffix.
5. How many ZCTAs cover each state?
A tab delimited text file listing ZCTA counts is available from the Census Bureau for download.
6. Is there a corresponding ZCTA for every for every United States Postal Service ZIP Code?
Based on the January 2000 list of ZIP Codes from the USPS's Delivery Type File, the ZCTA delineation process excluded 10,068 ZIP Codes in the United States and Puerto Rico (not counting overseas military ZIP Codes). These included 2,523 ZIP Codes that served specific companies or organizations with high volumes of mail and 6,419 ZIP Codes dedicated to Post Office (PO) Box and/or general delivery addresses primarily located in areas otherwise served by rural route or city style mail delivery. The remainder represents ZIP Codes that were either inactive or insufficiently represented in the MAF and therefore did not become ZCTAs.
New ZIP Codes created by the USPS since January 2000 will not have a corresponding Census 2000 ZCTA. Updated TIGER/Line® Files will contain updated ZCTAs which (while maintaining the restrictions mentioned above) will correspond to the October, 2002 list of ZIP Codes from the USPS's Delivery Type File.
7. Is there an equivalency or comparability data product that shows the relationship between Census 2000 ZCTAs™ (ZIP Code Tabulation Areas) and USPS 2000 ZIP Codes?
The Census Bureau did not produce a 2000 ZIP Code to 2000 ZCTA relationship file. They created the ZCTAs specifically to address the inadequacies of ZIP Codes for census data tabulation.
For those who may want to do this, the TIGER/Line® files will continue to show address ranges with mailing ZIP Codes. These files can be processed using a GIS to compare the ZCTA code for a block to the mailing ZIP Code associated with the address ranges on each block side. Such a comparison can provide a general idea of how the two relate.
The relationship between ZIP Code and ZCTA can be determined fully only by comparing individual block-geocoded addresses to the ZCTAs. This process is quite involved. Some examples of why the process can become quite involved are as follows: ZCTAs follow census block boundaries. In contrast, USPS ZIP Codes serve addresses with no correlation to census block boundaries; therefore, the area covered by a ZCTA may include mailing addresses associated with ZIP Codes that are not the same as the ZCTA.
A ZCTA may include a mailing address with a unique or PO Box ZIP Code that is ineligible to become a ZCTA. Addresses with PO Box ZIP Codes generally cluster around a post office, but they may be widely scattered across several ZCTAs. Consequently, the relationships that exist between ZCTAs and ZIP Codes can become quite complicated, so that within the boundaries of a single ZCTA there may exist several ZIP Codes; likewise, within the boundaries of a single ZIP Code, there may exist more than one ZCTA.
Some addresses included in the census and used to define ZCTAs (typically in rural areas) have incomplete or, in some cases, no mailing ZIP Code, thus making it difficult to determine the full extent of the relationships between ZCTAs and ZIP Codes.
8. Why are there ZCTAs for some dedicated PO Box ZIP Codes and not for others?
Dedicated PO Box ZIP Codes present a special challenge for ZCTA delineation. While addresses with these ZIP Codes generally cluster around a post office, they may also be widely scattered. Additionally, there may be the option of regular/street delivery present in the areas around these post offices, resulting in a mix of valid USPS ZIP Code options for residents.
For ZCTA delineation, the Census Bureau attempted to isolate those PO Box Only ZIP Codes for which there was a relatively compact, well-defined cluster of census blocks where the majority of residents chose or were required to receive their mail via PO Box delivery. For areas where the households receiving their mail via PO Box delivery are more widely scattered and intermixed with households receiving mail via regular/street delivery, the delineation process gives preference to the street delivery ZIP Code.
9. Do ZCTAs reflect commercial ZIP Codes?
The ZCTA delineation process included both residential and commercial addresses. A ZIP Code representing a commercial district may appear as a ZCTA if the ZIP Code serves the majority of the addresses for the census blocks in the area. However, individual firms or organizations with their own ZIP Codes are automatically excluded and do not become ZCTAs. There are 2,523 of these unique ZIP Codes excluded from Census 2000 ZCTA delineation.
10. What do the ZCTAs with an "XX" or "HH"suffix represent?
The three-digit ZCTA code and an "XX" suffix are applied to a large land area (generally larger than 25 square miles) where we had insufficient information to determine the five-digit codes. The USPS may not provide five-digit ZIP Code delivery service in this area. These are generally rural areas with little settlement; for example, parks, forest lands, and desert and mountainous areas. Smaller areas were generally absorbed into adjacent five-digit ZCTAs, but for larger areas, the Census Bureau did not want to overextend the surrounding five-digit ZCTAs.
The requirements for ZCTA delineation state that all census blocks receive a ZCTA code. Because large water features may border many five-digit ZCTAs, it would be difficult to divide up the water features and assign the parts to the five-digit ZCTAs on the land. Furthermore, any attempt to add these water features to land-based ZCTAs, would greatly distort the size and shape of the land ZCTAs, particularly in coastal areas. To avoid these problems, such water features receive ZCTA codes ending in "HH" (special code for hydrographic features).
11. Why do some water features have a distinct ZCTA Code?
The requirements for ZCTA delineation state that all census blocks receive a ZCTA code. Because large water features may border many five-digit ZCTAs, it would be difficult to divide up the water features and assign the parts to the five-digit ZCTAs on the land. Furthermore, any attempt to add these water features to land-based ZCTAs would greatly distort the size and shape of the land ZCTAs, particularly in coastal areas. To avoid these problems, such water features receive ZCTA codes ending in "HH" (special code for hydrographic features). Note that a single code could not be used for all water areas for data processing reasons.
12. Why do some ZCTAs ending in "HH" contain land area?
After Census 2000, efforts to improve the spatial accuracy of the TIGER database have and continue to add land area such as small islands or sections of shoreline to census blocks that were entirely water in Census 2000. Census 2000 tabulation census blocks once consisting entirely of water features may now contain a mix of water and small land features. As a result, "HH" ZCTA codes may no longer represent purely water areas.
13. Why does the census block where I live have a different ZCTA than my ZIP Code?
ZCTAs are approximations of mailing ZIP Codes and should not be confused with them. There are some common reasons why someone's ZIP Code may not match the ZCTA code:
1. Your block may contain addresses with another ZIP Code, and the majority of addresses in the block have this other ZIP Code;
2. Field operations may not have been able to identify a ZIP Code for all addresses in your block during the census. Where information was incomplete, the ZCTA delineation process used the available information or extended the ZCTA codes to your block from a neighboring area; and
3. The Census 2000 ZCTAs will exclude some ZIP Codes:
- ZIP Codes unique to firms, organizations, and institutions that represent a single delivery (the institution or firm may cover a large area or have many locations, but the delivery is generally made to one place);
- Dedicated PO Box ZIP Codes that appear in areas that are also served by either city-style, highway contract, or rural route delivery;
- ZIP Codes that are not valid for that state and county;
- Discontinued ZIP Codes;
- General Delivery ZIP Codes.
Based on the January 2000 list of ZIP Codes from the USPS's Delivery Type File, the ZCTA delineation process excluded 10,068 ZIP Codes in the United States and Puerto Rico (not counting overseas military ZIP Codes). These included 2,523 ZIP Codes that served specific companies or organizations with high volumes of mail and 6,419 ZIP Codes dedicated to PO Box and/or general delivery addresses primarily located in areas otherwise served by rural route or city style mail delivery. The remainder represents ZIP Codes that were either nonactive or insufficiently represented in the MAF and therefore did not become ZCTAs.
14. What is the relationship between ZCTAs and other statistical areas (such as census tracts) or governmental entities (such as places and counties)?
ZCTAs almost always exist within a single state but are independent of all other statistical and governmental entities except Census 2000 tabulation blocks. While data from the USPS may indicate that a given governmental entity is serviced by a single ZIP Code, that should not be taken to indicate that every household in that entity is serviced by that particular ZIP Code, nor that the indicated ZIP Code services only those addresses located within the boundaries of that governmental entity.
Final Census 2000 ZCTA statistics showed that 27 percent of ZCTAs cross county or county equivalent boundaries nationwide. There are 47,010 unique ZCTA-county combinations (32,038 are five-digit ZCTAs). Of these five-digit ZCTAs, 42 cross state boundaries.
15. Is it possible to get a ZCTA-to-block or ZCTA-to-entity relationship file?
The Census 2000 and subsequent TIGER/Line® files provide geographic descriptions of the legal and statistical entities included in census tabulations. By linking together data from the TIGER/Line® files, data users will be able to generate a wide range of ZCTA-to-block or ZCTA-to-entity relationship data. In addition, the Census Bureau is providing a ZCTA-to-Metropolitan Statistical Area (MSA)
relationship file for download.
16. Why do some ZCTAs form discontiguous areas?
Discontiguous parts of ZCTAs may represent offshore islands. In other situations, they may result from using census blocks to build ZCTAs. United States Postal Service (USPS) carrier routes tend to extend out along the local street network. Addresses along a street may have one ZIP Code while addresses along the cross streets have another. If a block is characterized by addresses with the ZIP Code of the cross streets it may isolate a another block characterized by addresses of the first ZIP Code, and it becomes a discontiguous area. Joining the fragments by changing the ZCTA code for intermediate blocks could degrade the match between ZIP Code and ZCTA. Rather than degrade this match, the ZCTA coverage retains some discontiguous fragments.
17. Why are there instances of fragmented or discontiguous three-digit ZCTAs?
The USPS may assign several three-digit ZIP Codes to the areas around some cities. The five-digit ZIP Codes within these areas are distributed across the area and do not form specific three-digit clusters. To identify these areas see the USPS maps of three-digit ZIP Codes, located in the 2000 National Five-Digit ZIP Code and Post Office Directory USPS publication 65. The maps show certain areas with multiple three-digit ZIP Codes. For an example, see the area around Cedar Rapids, Iowa with the three-digit ZIP Codes 522 and 523.
If the fragmented areas are problematic for your application, you might try to do what the USPS does in the Publication 65 maps and aggregate the fragmented three-digit areas into a single combined area.
18. Are there size limitations to ZCTAs?
Currently, there are no restrictions limiting how large or small a ZCTA can be in terms of either a minimum/maximum number of housing units or geographic area. ZCTAs reflect the areas where we find addresses with the specified ZIP Code. As a result, ZCTAs may be as small as a few city blocks or cover many square miles.
19. Does the Census Bureau have any data available on land area per ZCTA?
The downloadable ZCTA gazetteer files
contain the total land and water area (in square kilometers and in square miles) for each Census 2000 ZCTA.
You can also extract this information for three- or five-digit ZIP Code Tabulation Areas from the Advance National Summary File 1 geographic header file.
The geographic header file is the last file in the list (usgeo_u1.zip). Extract summary level (SUMLEV) 850 for three-digit ZIP Code Tabulation Areas, and summary level 860 for five-digit ZIP Code Tabulation Areas. The area measurements are expressed in square meters. Be sure to read the "File Structure README" and the "0README_SF1.doc" for a more complete description.
20. How can I find coordinates (Latitude and Longitude) for ZCTAs based on centroid?
The downloadable ZCTA gazetteer files
contain the latitude/longitude coordinates for each Census 2000 ZCTA. Coordinates for ZCTA internal points (calculated by considering the latitude/longitude of all bounding features and then creating an area-weighted average point inside the polygon) are also available in the TIGER/Line® Files
21. Are the 1990 census statistics reported by ZIP Code comparable to the Census 2000 results by ZCTA?
Even though the codes may appear the same, the addresses and areas covered by these areas may not be the same. We strongly advise data users who wish to compare 1990 and 2000 data to determine and evaluate any coverage differences that exist before making any comparisons. There are several reasons for this caution:
- The USPS has extensively modified ZIP Codes over the last ten years. Even though a 1990 ZIP Code matches a Census 2000 ZCTA code, there is no guarantee that these cover the same geographic area. Also, some ZIP Codes in the 1990 data products were discontinued by the USPS, and new ZIP Codes were created;
- ZCTAs and the 1990 Census ZIP Code areas were delineated using different methodologies and therefore may not have comparable coverage area or size; and
- The Census 2000 ZCTAs will include some dedicated PO Box ZIP Codes. All dedicated PO Box ZIP Codes were excluded as ZIP Code areas in 1990. The resulting 1990 areas include data for both PO Box ZIP Codes and the ZIP Codes that provide street or rural route delivery to the surrounding area.
22. Are there plans to update ZCTAs in the future?
The United States Postal Service (USPS) makes periodic changes to ZIP Codes to support more efficient mail delivery. Therefore, the original Census 2000 ZCTAs may no longer match current ZIP Codes. For example, as a result of the updates in 2003, 581 ZCTAs were eliminated and 735 new ZCTAs were created, for a new nationwide total of 33,322 ZCTAs. Of that total, 32,227 ZCTAs carried the full five-digit numeric ZIP Code. The remaining ZCTAs had generic codes ending in either “HH” or “XX” suffixes.
The U.S. Census Bureau also adjusted ZCTA boundaries to account for new growth and more precise ZIP Code information, and modified some of the generic “XX” and “HH” ZCTAs to reflect expansion of five-digit ZCTAs and to achieve more consistent “XX” and “HH” coverage within and across county boundaries.
The U.S. Census Bureau did not re-tabulate data or produce statistical estimates for the updated ZCTA boundaries for dissemination through the American FactFinder Internet Site or revised Summary Files.
23. Will the Census Bureau create nine- or seven-digit ZCTAs?
ZCTAs are generalized approximations of USPS five-digit ZIP Codes. There are no plans to create subdivisions of five-digit ZCTAs that approximate the USPS ZIP+4 sector-segment codes.
24. How can I acquire ZCTA Maps?
ZCTA information is currently available in the following GIS formats: ArcView Shape .shp, ARC/INFO export .e00 and ARC/INFO Ungenerate ASCII. You can access these generalized
ZCTA cartographic boundary files from the Cartographic Boundary files web page.
Other sources include:
- Census 2000 TIGER/Line® Files: ZCTAs for the entire United States and Puerto Rico are available in the Census 2000 TIGER/Line® files. ZCTAs are stored in Record Type S, which stores codes that relate to TIGER polygons.
- 2003 TIGER/Line® Files: Updated ZCTAs reflecting USPS ZIP Code changes through October 2002 will be available in the 2003 TIGER/Line® files.
- American FactFinder Internet site:
Users can plot Census 2000 ZCTA maps and create tables showing census data tabulated by ZCTAs.
- Cartographic Boundary Files: Generalized boundary files, including ZCTAs are available for downloading in the following formats: ARC/INFO Export (.e00), Arcview Shape (.shp), and ARC/INFO Ungenerate ASCII. These files are appropriate only for small-scale thematic mapping.
- LandView®: LandView® is a desktop mapping system that includes database extracts from the Environmental Protection Agency, the U.S. Census Bureau, and the US Geological Survey. These databases contain ZCTA boundaries along with jurisdictional boundaries, roads, rivers, and railroads, census block groups and census tract polygons, and a variety of landmark features. LandView is available on DVD (Digital Versatile Disc) data disks with geographic files for the entire country (all 50 states, the District of Columbia, and Puerto Rico). The software will run on both Windows and Macintosh computers.
Some points of note:
- In most instances the ZCTA code equals the ZIP Code for an area
- In creating ZCTAs, the Census Bureau took the ZIP Code used by the majority of addresses in an area for the ZCTA code; some addresses will end up with a ZCTA code different from their ZIP Code.
- Some ZIP Codes represent very few addresses (sometimes only one) and therefore will not appear in the ZCTA universe.
- The term ZCTA was created to differentiate between this entity and true USPS ZIP Codes.
- ZCTA is a trademark of the U.S. Census Bureau; ZIP Code is a registered trademark of the U.S. Postal Service.
- The Census Bureau does not have U.S. Postal Service ZIP Code boundary files, nor do they have information or possible sources of such files.