Master Area Geographic Glossary Of Terms — 2014

Revised November 2018

This web page documents and summarizes geographic entities used in the 2014 edition of the MABLE database, accessible via the Geocorr 2014 web application. It is specifically geared towards the geographic entities as they are used in this web application, but also includes general explanations of thevarious geographic types. For a more offical document describing the 2010 geographic entities, see the 2010 Geographic Terms and Concepts page at the Census Bureau web site.To see base maps for many of these entities (primarily the ones used for tabulating the 2010 census and/or the American Community Survey) see the Bureau's reference maps page.

Geocode index:


The geographic coverages are presented here as they appear on the Geocorr 2014 select lists for source and target geocodes. The majority of codes are based on the 2010 decennial census, specifically the geographic header files that came as part of Summary File 1. As such, they are vintage January 1, 2010. But we do have geocodes that are more recent, and these will be explicitly identified.

The Missouri Census Data Center and OSEDA maintain a library of geographic codes in the form of SAS format codes. These formats have special application for SAS software users, since they allow codes to be readily converted to their corresponding names. Sometimes format modules are used not to provide names, but rather to link codes to other entities as a kind of table lookup.

In the text below when a SAS format is available for a geocode, we provide a link to it at the end of the entry for that code. Rarely, but in a few instances, there may be entries in the format code that do not appear in the MABLE database. For example. the $fipstab format code contains entries for Puerto Rico and U.S. territories (Guam, Virgin Islands, etc.) that are not in MABLE.

Most of these geographic codes comprise numeric digits, but they have no numeric significance. They are stored in the MABLE database as character strings rather than binary numeric fields. In reports they will display with leading zeroes (01 as the code for Alabama, for example, rather than just 1), and these leading zeroes also are written to output CSV files by the Geocorr application.


Format tables: and

The MABLE database is really a collection of 51 state-level databases. The state geocode is almost always added to output files even if it is not explicitly selected. The District of Columbia is considered a state for the purposes of this application. Other statistically equivalent areas, such as territories and outlying areas (including Puerto Rico) are not states and are thus not part of MABLE. This is a two-digit FIPS (Federal Information Processing Standard) code with leading zeroes.


Format table:

The FIPS county codes are three-digit numbers assigned within states. They generally are odd numbers assigned in alphabetical order. Exceptions are independent cities (i.e., cities like Baltimore and St. Louis that are not in any county and serve as county equivalents), which are usually assigned codes over 500 (such as 510). On output files and listings, we usually combine the FIPS state and county codes. Thus, the value of the County variable for Autauga County, Alabama is 01001 and for Baltimore City, Maryland is 24510. In some states (such as Louisiana and Alaska), the primary substate legal entities are not called counties; but for the sake of this application they are county equivalents and act exactly the same as counties.

Counties appearing here are those defined at the time of the 2010 census. However, there is also a 2014 county option in the Geocorr application, due to a minor change in 2015. (See below.) See the Census Bureau web page describing any changes that may occur. There are approximately 3,143 counties in the U.S.

County Subdivisions (MCD-CCD)

Format table: (returns the county subdivision name, but not the county)

These are the primary geographic units recognized by the Census Bureau which are just below the county level. Most states have minor civil divisions (MCDs), which are legally recognized governmental or administrative units. MCDs are defined in 28 states and in D.C. In the remaining states the Census Bureau has defined Census County Divisions (CCDs). Most states have either all MCDs or all CCDs (with Missouri being an example of a state that has both). "MCD" is a generic category; the specific types of MCDs vary by state. The most common type of MCD is the township. Other types of areas that can be MCDs include towns or incorporated places, election districts, plantations, magisterial districts, etc. In the geographic hierarchy, these divisions provide a complete coverage of all counties in the country. There were 35,703 such geographic areas in the U.S. at the time of the 2010 census.

This excerpt from the technical documentation released with the 2010 PL94 files summarizes some of the odd and inconsistent (across states, at least) behavior of these entities:

In some states, all or some incorporated places are not part of any MCD; these places are termed independent places. Independent places also serve as primary legal subdivisions and have a Federal Information Processing Series (FIPS) county subdivision code and National Standard (ANSI) code that is the same as the FIPS and ANSI place code. In nine states — Maine, Massachusetts, New Hampshire, New Jersey, North Dakota, Pennsylvania, Rhode Island, South Dakota, and Wisconsin — all incorporated places are independent places. In other states, incorporated places are part of, or dependent within, the MCDs in which they are located, or the pattern is mixed — some incorporated places are independent of MCDs and others are included within one or more MCDs.

On output files and listings generated by Geocorr, this variable goes by the name cousubfp ("COUnty SUBdivision FiPs").

Place (City, Town, Village, etc.)

Format tables:

Lots of variety exists for this geographic level. Places have different names in different states (e.g., "cities", "towns", "boroughs", "villages", etc.) There are also 9,721 entities called census designated places (CDPs) which have no formal, legally recognized boundaries but which the Census Bureau has designated as areas which are worthy of having data tabulated for them. Places are within states, but otherwise they can cross just about any other boundary. Places are mutually exclusive but are not exhaustive — there are areas that are not contained in any place. The Census Bureau (and MABLE) assign a code of "99999" to areas that are not within any place. These "pseudo-places" are simply referred to as unincorporated remainders; they are not simply "unincorporated portions" (in general), because in many cases part of the unincorporated area of a county or MCD is in a CDP.

The relationship of MCD-CCDs (county subdivisions) and places varies from state to state, but in general places may cross MCD-CCD boundaries. There are some places which are also MCDs (common in New England). In these cases, the FIPS MCD and place codes are the same (but not the census codes). There were 29,261 places recognized for the 2010 census.

Note: Places are among the most unstable of geographic entities over time, and are perhaps the most difficult to identify accurately since their boundaries are often "invisible" — i.e., do not follow physical features that are easily identifiable. Because of this, the Census Bureau has a real challenge trying to keep up with accurate place definitions. The codes used in MABLE come from the Bureau's official SF1 geographic headers files, which define the geography of the United States as of 1-1-2010. The place codes that appear in MABLE reflect what the Bureau recognized for city boundaries when it tabulated the 2010 census. It is an accepted fact that there will always be mistakes regarding these boundaries. The Bureau has published a special file called the CQR (for "Census Quality Review") that is the official list of known geographic coding problems. MABLE now includes a "current" place code (as of 2014), described below. The place-based category pseudo-codes place size catgory and within-a-place code are still based on 2010 geography, as is the census place code.

Current (2014) geocodes

We have added these three geographic codes based on data in the 2014 TIGER Line Faces data. Each record in MABLE 2014 corresponds to a 2010 block; this is not going to change until we move to a 2020 block base which is still several years away.

As of July, 2015, the 2014 county differs from the 2010 county for only a single county in the U.S. That is Bedford County, VA (51019), which now includes the city of Bedford. The latter was formerly an independent city (with county code 51515); the change occured in 2015.

The county subdivision and place codes have 2014 versions available here. Note that place-size and within-a-place category codes have NOT been updated to reflect place-geography changes since 2010.

New values for school districts and metro areas have also been added, and are discussed elsewhere in this document.

Census Tract (2010)

The census tract is part of the very useful four-level hierarchy of census data, in which each lower level is completely contained within its parent level. The four levels are county, tract, block group, and block.

The Census Bureau has complete control over these "small-area" geographic units. The Bureau defines them solely for the purpose of collecting and tabulating the results of the census. In most metropolitan areas, local census tract committees are appointed which are responsible for drawing up suggested boundaries for the census tracts in their areas. In most rural areas, there can be (but usually are not) such committees, and the Census Bureau defines the tracts. In the 1990 census, areas that were defined without the input of a local tract committee were called block numbering areas (BNAs), but this terminology was dropped in 2000, and everything since then is called a census tract.

Among the criteria that the Census Bureau has established for defining tracts is that they should be compact contiguous areas with populations of about 4,000 persons and that the area should, if possible, be homogeneous. The ideal urban census tract would be a locally recognized "neighborhood" within a city. Prior to 1990, census tracts were strictly an urban concept; they were only defined within metropolitan areas.

Census tracts are assigned four-digit numeric codes, unique within counties. Tracts can also have a two-digit suffix code, usually indicating that this is a "split" of a tract from an earlier census year. Thus if 1234.00 was a tract in 2000 with 5,000 persons and that area grew to a population of 12,000 by 2010, you might see three tracts in 2010 with codes 1234.01, 1234.02, and 1234.03. Suffix codes of .97 and .98 are special and have to do with details most people would rather not be bothered with. The short explanation is that it represents where there was a "temporary problem" with a tract assignment that was "fixed," but this suffix code had to be attached. Suffix codes of .99 are used for pseudo-tracts used to tabulate "crews of vessels" residing in nearby rivers and lakes.

Census tract codes on all output files and reports form Geocorr are named tract and are always represented in a full seven-character xxxx.xx format with leading and trailing zeroes. There were about 74,134 of these entities defined for the 2010 census.

Whenever you select this geocode (using Geocorr) from either the source or target geocode select lists, the county code is also automatically selected for you — you should never process tract data without carrying along the county code, unless, of course, your entire analysis is taking place within a single county.

Tracts do not have names associated with them, in general, and there are no format codes available for them. Tracts do not generally have to nest within any other geographic areas except counties and PUMAs.

Block Group (2010)

If you understand census tracts, then all you need to know is that block groups are the next level down in the hierarchy. A typical census tract will be comprised of about five or six block groups. The name comes from the fact that each block group (BG) is composed of census blocks, grouped together within a tract. The first digit of the four-digit block number is the code for the area. Thus the block group geocode is only one character long, which, of course, is meaningless outside of the context of the tract and county. Block groups with a code of 0 indicate a coastal area entirely comprising water.

From a data perspective, block groups have the distinction of being the smallest geographic unit (well, almost) for which the Census Bureau tabulates detailed demographic data. This means that if you are looking for data regarding income, occupation, or education (to name three popular subjects only available in the sample data) then the smallest geographic unit for which you'll be able to get that data is the block group. In the past, these data would have been from the decennial census, but that changed starting with the 2010 census. "Long form" data is no longer collected in the decennial census. Those data are now obtained as part of the American Community Survey. ACS data at the block group level is available, albeit not very conveniently and with significant amounts of sampling error in many cases.

On all Geocorr output files, this geocode will be called bg and will be a single character (digit) long.

Block groups do not have names associated with them, and there are no format codes available for them.

Census Block (2010)

This is the atom of the MABLE database. It is the smallest geographic entity recognized by the Census Bureau. It is generally the smallest area that can be formed by intersecting visible features. The classic census block is the rectangular city block bounded by four streets. With the extending of block assignment to rural areas for the 1990 census, we also now have the 100-square-miles-of-open-desert blocks and the classic single farm or portion of farm block. Each of the over 10 million observations on the MABLE database describes one census block. All other geographies are defined in terms of which of these blocks can be added together to form it. This is a fudge in some cases — notably with ZIP (ZCTA) codes, but makes perfect sense for most geographies. This is because the Census Bureau made a decision when it redesigned census block geography for the 1990 census (and beyond) that it would not have any blocks that crossed county subdivision or place boundaries. The Geocorr concept is based on the idea that geography can be reduced to a set of block-level "pixels" that can be used to examine how other geographies are related using simple algebra instead of complex geometry.

Census blocks are the last level of the county-tract-bg-block hierarchy. The block code itself is four digits (the first of which, as mentioned above, indicates the block group.) If the first digit is 0, it indicates a water block, which as the name implies is located under water and rarely has anyone living in it. These water blocks were not included in the 1990 version of MABLE but are now. They tend not to contribute much, however, since they have almost all 0 values for the weight variables (population, households, and land area).

On all output files and listing produced by Geocorr, the census block geocode is called blk and is four characters long. Census blocks do not have names associated with them.

Five-digit ZIP / ZCTA (2010)

Format table:

For the 2000 Census, the Census Bureau decided to change the name of the geographic entity that they had previously referred to as ZIP codes. They would now be called ZCTAs (ZIP census tabulation areas). There were rather minor changes in the way these entities were defined as compared to 1990, but the Bureau decided that it would be helpful to alert the users to the fact that these entities were not exactly ZIP codes. But, for most purposes, pretty close. To see the definitive word on the what, why, and how of ZCTAs see the Bureau's ZCTA web page or the Geographic Terms and Concepts - ZCTAs web page.

Only "residential" ZIP codes — those containing household addresses — have corresponding ZCTA codes (and hence will appear in a MABLE database). There are no business or PO-box-only ZCTAs, etc. The latter account for about a fourth of all ZIP codes in the U.S. You can view/download a CSV file that shows all ZIP codes (vintage 2010) to the corresponding ZCTA. (Uexplore/Dexter users can access the same data in the corrlst.zip_2_zcta10 data set.)

Another problem is that ZIP codes are not really spatial entities — they are simply lists of addresses, organized to facilitate mail delivery. While they often do form areas that can be viewed as geographic areas, that is not what they really are. This can create problems when you try to relate them to a spatial entity such as a census block. Think of a classic census block formed by the intersection of 1st St., Elm Ave, 2nd St., and Pine Ave. If 1st St. is the northern border of the block, then folks living on the south side of 1st St. between Elm and Pine are in our block (let's call it "101"). But people living across the street — on the north side of 1st St. — are living in a different block, say "102". But the U.S. Postal Service would never have a ZIP boundary go down the middle of a street. If this were an area where the ZIP changed, it would almost certainly divide along (vague and invisible) "back-lot lines." For example, the folks living on both sides of 1st St. in our example might live in ZIP 12345, while the folks living on 2nd St. might live in 12346. Thus you have households in the same census block, but in different ZIP codes. Hence, the fundamental concept of census block as the atomic unit is violated. Of course, this only happens in a certain percentage of blocks, and in many cases the ZIP boundaries are on commercial streets where not many people live and you can assign most of the population in the boundary blocks to the right ZIP. These issues are dealt with in the Bureau's definitive web page (see link above) that describes how these issues were dealt with when defining ZCTAs.

On output files, this geocode is stored as ZCTA5. The variable Zipname is also included (unless otherwise requested). This name has undergone a number of changes over recent years (2010-2013) and the current value matches the value of the zipname variable in the zcta_master data set (in /pub/georef).

Pseudo-ZCTA codes ending with XX or HH (e.g., 594XX and 594HH in Montana) were used to designate unassigned (to any ZIP code) and water-area blocks for the 2000 census. They have been dropped for 2010 and hence will no longer appear in Geocorr's output. You will see them in Geocorr 2000 results.

To get information regarding any ZCTA (or even non-ZCTA ZIP) the MCDC offers the ZIP Code Lookup web application.

For more information about ZIP codes, see the MCDC's ZIP Code resources page and its updated companion piece ZIP Codes 2010 supplement with its link to the zcta_master data set.

This format code was derived from a file from the U.S. Postal Service circa 2010. It's a combination of post office and local geographic names. It is the source for the ZIPNAME fields that will be added to your Geocorr outputs if you select ZIP as one of your geocodes.

Concentric Ring Pseudo-Geocode

This is not exactly a geocode in the same sense as most others used here (urban-rural portion is another exception). These are geographic areas determined on the fly when the user specifies the coordinates of a point (in the Point and Distance Options section of the form, and also selects Concentric Ring Pseudo-Geocode (CRP-G) from either the source or target geocode select list. Suppose, for example, the user enters "1", "3", "5", and "10" in the #1, #2, #3, and #4 text boxes in the P&D section of the form. This means they want to look at data for the one-mile circular area around the specified point, and then also at the ring (donut: a circle with a hole in the center) greater than one mile but less than or equal to three miles from the specified point, and also the ring from three to five and a final one from five to 10. By convention we assign a code to identify the concentring ring equal to its outermost radius. In this example, the values for the CRP-G would be 1, 3, 5, and 10. Notice that the area represented by the code "10" is not a 10-mile circle; it is a donut formed by taking a 10-mile circle and subtracting out the five-mile circle with the same center point. To just get the 2010 census population figures for each of these areas you can select "CRP-G" as the source geocode, and "Entire Universe" as the target code.

Urban-Rural Portion

This is not exactly a geocode in the same sense as the other ones used here, but it is far too useful to discard on a technicality. All census blocks are assigned this characteristic by the Census Bureau based on their standard definition of the concept of "urban." That definition can get rather complicated when you follow it down to the source, and it has changed over time. See our Ten Things to Know About Urban vs. Rural page for almost all you need to know about this topic. The assignment of these values is based on very detailed (i.e., block level) data from the most recent decennial census. These values are typically not published until the year ending in "2" following a decennial census. Which is why we specify "2012" as part of the identifier of this field in the Geocorr 2014 application. It is actually the definition as of 2010, but we were only able to access this information starting in 2012. The definitive source of information regarding the concept is the Census Bureau's Urban and Rural Classification page. And, in December 2016, the Bureau created this Story Map that provides a nice historical perspective on the urban-rural concept, suitable for children.

This geocode has two values: U means urban and R means rural. On Geocorr output files, this field is called ur and is one character long. There is no name field associated with it.

Urbanized Areas/Urban Clusters (2010)

Format table:

We referred to these entities above in our discussion of urban/rural. To be urban starting with the 2000 census is be part of an urbanized area or an urban cluster. These two entities share a variable on the MABLE database and a set of five-digit codes. The only difference between them is the size of its densely settled core that is the primary requirement that must be met before an area can be considered urban. That densely settled core area must have a population of at least 1,000 persons per square mile and must have a total size of 10,000 persons. If it is over 50,000, then you have an urbanized area; if it is between 10,000 and 49,999, then you have an urban cluster. The area comprises this central core plus the surrounding contiguous area with a density of at least 500 persons per square mile. There are some important exceptions to these general rules (to allow for special situations where there may be "hops" across certain bodies of water or "green belts".) See the Census Bureau's FAQ page on the subject.

On all Geocorr output files, this field is called urbarea and is five characters wide with leading zeros.

UA and UC codes are included in the MCDC's geographic codes lookup web app.

PUMAs for 5% Samples (2000 and "2012")

Format table: (2012 codes only)

PUMA (public use microsample areas) are a special Census-Bureau created geography designed for use as the smallest unit of geography that is identified on their Public Use Micro Sample ("PUMS") data products. They are redefined for each decade, for use with the PUMS files that are released based on that decade's PUMS products. It has gotten a bit more complicated now that we have the American Community Survey, with its own PUMS files and the strong interest now in summary data using PUMAs as the unit being summarized. The increased interest has to do with the key fact that PUMAs have as a basic requirement a population of at least 100,000 per the census to which they pertain. A 2010 PUMA (also referred to as "2012" for reasons we go into below) must have a 2010 population count (not an estimate — a decennial census 100% count) of at least 100,000. This means that they all meet the 65,000 population threshold used in the ACS to qualify an area for getting single-year ACS data. There are very few geographic levels for which completely new ACS data are released every year. The PUMA turns out to be the smallest unit about which this can be said. They have the added assets of being relatively equal in terms of total population and of staying put for a predictable period of ten years.

Most of what you can say about 2000 PUMAs can be said about 2010 PUMAs. There is one significant difference, however. For 2000, PUMAs could be defined in terms of incorporated place boundaries. So, for example, the city of Springfield, MO was used as the exact boundary of a PUMA (with a complementary PUMA being defined as the remainder of Greene county, in which the city is located.) The Census Bureau decided for 2010 that they did not want to allow corporate limits to be used in setting up the definition of PUMA boundaries. Because such boundaries can and do change over the decade. The Bureau thus issued the edict that starting in 2010 PUMA boundaries could be specified only in terms of census tracts or whole counties. Things which almost always stay put for ten years.

PUMA codes are five digits (characters) long. Most end with 00. Generally when the last two digits are not zeroes, it represents a county that has been split into subareas. Thus, for example, the 2010 PUMA codes for the St. Charles county (MO) are 01701, 01702, and 01703.

On all Geocorr output files these fields will be called puma2k or puma12 and will be five characters wide with leading and trailing zeroes. There will be no names associated with the 2k PUMAs except in Missouri. Names will be provided for the 2012 codes, since the Census Bureau allowed the states to name the PUMAs starting with the 2010 versions.

There are also codes called super PUMAs (aka "1% PUMAs") that were used on the 2000 PUMS 1% sample files. These have never been kept on the MABLE database and we have no plans to add them.

For more about these entities you can view our All About PUMAs web page.

Core Based Statistical Area (CBSA)

Format table:

This is the current geocode to use when you want to have data for a metropolitan area or a micropolitan area. These entities are sometimes referred to as MSAs (metropolitan statistical areas) by the Census Bureau. We understand why they do this, because people feel more comfortable with the MSA acronym/label. Only trouble with it is that a micropolitan statistical area is now also a metropolitan statistical area, even though strictly speaking those two entities are mutually exclusive.

Note that this field has a year specified. We currently have the 2013 vintage (last modified by OMB as of February, 2013) CBSA and related codes (CBSA type, metropolitan division and combined statistical area). These are county-based areas and new ones can be added, old ones modified, deleted, renamed, etc. each year. The "core based" portion of the name derives from the was these areas are defined. They require a densely populated "core area"of at least 10,000 people. The core area must be at least 50,000 to qualify as a metropolitan SA; otherwise it is called a micropolitan SA. These areas are usually named for the largest incorporated areas (central cities) that form all of portions of the core area. CBSAs are comprised of counties containing or adjacent to their core areas. The basic criteria regarding which counties are included in the CBSA involves the number of people living in the non-core counties who commute to work within the central county (counties).

CBSAs have a five-digit code. Metropolitan and micropolitan areas share the same pool of codes; you cannot tell from the CBSA code which kind it is. (That is why we have the CBSA type as a separate geocode.)

For more about these and related geographic entities see the Census Bureau's core based statistical areas and related statistical areas web page.

As already mentioned, CBSAs (almost always) comprise complete counties or county equivalents (parishes, independent cities, etc.). There is only one exception to this general rule: The portion of the city of Sullivan in Crawford County, MO was legislated to be part of the St. Louis metropolitan area. It has to do with a veterans' hospital being located there and something about a formula for federal subsidies in metro vs. non-metro areas. As of July, 2009, there were approximately 1,500 people living in this area.

CBSA Type (Metro or Micro)

Used to distinguish metropolitan vs. micropolitan statistical areas. The three possible values are "Metro", "Micro," or blank (when CBSA is blank, so is this field). Having this field is handy for letting you generate reports that show the latest population estimates by state for the metropolitan, micropolitan, and "neither" portions of a state. It is generally a good idea to keep this geocode whenever you keep CBSA, since the CBSAname field will not include the type (i.e., you get "Columbia, MO", not "Columbia, MO Metropolitan Statistical Area"); thus you need this field to complete the full name of the metro area (CBSA).

Metropolitan Division

Format table:

Some core-based MSAs are large enough that they have significant subareas comprised of related counties. These subareas are called metropolitan divisions, and they have their own five-digit FIPS codes. An example is the Chicago-Naperville-Joliet, IL Metropolitan Division, which is the Illinois portion of the tri-state Chigago core-based MSA. This would be comparable to a PMSA under the previous MSA-CMSA-PMSA scheme. There are not very many of these.

Combined Statistical Areas

Format table:

Same concept as the metropolitan divsision except that here we are talking about a combining of CBSAs into a larger geographic area. Note that all thse CBSA-related geocodes get updated in sych so they are all the same vintage.

Note that the code 426 was used for Peoria-Canton, IL until as part of the July 2015 update, it was changed to now pertain to Pensacola-Ferry Pass. FL-AL. So we updated for $csa format code to display Peoria-Canton, IL or (as of 7/15) Pensacola-Ferry Pass, FL-AL.

New England City and Town Areas (NECTA)

Format table:

They always have to be different in New England, where counties are disdained and towns are what count. So while they passed a law saying that all CBSAs would be county-based, they could not force the good people of New England to actually use those entities. Instead, the powers that be agreed to create alternative metro area definitions using the core-based technology (i.e., the central densely setttled area not constricted by any municipal boundaries) but with towns ("MCD"s) as the component units rather than counties.

NECTA Divisions

See metropolitan divsion, above. NECTA divisions are to NECTAs as metropolitan divisions are to CBSAs. They are town-based subareas of NECTAs.

Metropolitan/Micropolitan and Related Codes as of ...

These metro area definitions are updated on an irregular basis throughout the decade. These code stayed unchanged from the time of the 2010 census until February of 2013. And then, just as we were doing our update for MABLE 2014 there was another update that was effective as of July, 2015. There are actually a set of five codes that reflect a new set of metro area definitions. The basic metro area (or CBSA, core based statistical area), the CBSA type (metro or micro), metropolitan divisions (sub-CBSAs) and combined statistical areas (super-CBSAs), and the Central code indicating whether the county is considered a central county of the CBSA. There are two sets of these five codes, one for the 2013 vintage and one for the 2015 definitions. We do not as a rule attempt to maintain geographic time series in MABLE, but these codes are of sufficient interest that we made an exception.

Voting Tabulation Districts (VTD)

Anyone involved in redistricting will recognize these units, and anyone not involved in redistricting is unlikely to be very interested. These were geographic entities that the states identified and labeled back in 2009 so that in 2011 the Census Bureau would deliver basic population data for these geogaphic units which could then be used as the building blocks for the state's congressional and state legislative districts. These can be anything the state (or the local entity within the state — things can vary widely within a state) wanted them to be but typically they correspond to precincts or other voting units. The codes assigned can be mnemonic (i.e., related to the codes for the precints or wards to which they correspond) or arbitrary (as in most of Missouri). The real ID in many cases is in the corresponding VTDName field. The Bureau wrote guidlelines for how the states were to assign the codes but they were largely ignored in Missouri. The codes in that state — or at least for many counties within it — were just sequentially assigned and stored as left-justified character strings (in direct violation of the guidelines). So, for example, the VTD code for Boone County, Precinct 34 is 39, while the correponding VTDName field has the more useful value "Voting Dist 34." On the other hand, in Cook County, IL, if the code is 03039, it turns out the area is Ward 3, Pct 39.

Congressional Districts

We have these codes for five congresses. The most recent is the 116th congress, elected in the fall of 2018. The 111th Congress, which was elected in 2008, was the Congress that was "current" at the time of the 2010 census, which is why we keep it. Data from the 2000 census published at the CD level summarizes the 111th vintage CDs.

State Legislative Districts

These are the districts which were redrawn circa 2011 using results (block level pop counts) from the 2010 census. These are the redrawn state districts in all states (as they appeared in the TIGER LineFaces datasets as of July, 2012). The "Upper Chamber" is referred to as the "Senate" in most states, while the "Lower Chamber" is usually called the "House" (in California it is called the "Assembly.") Nebraska has a unicameral legislature (meaning they have only one state legislative body instead of the usual two). The codes for the Lower Chamber districts are blank for Nebraska. These are three-digit codes with leading zeroes, even though in most states just one or two digits would suffice. There are no names associated with the codes.

The 2010 districts are those that were in effect at the time of the 2010 census. So,these are the old state districts that were superseded by the results of redistricting following the 2010 census.

Stage legislative districts may change every couple of years, although for most states there are no changes. We also now have state legislative districts for 2014 and 2016.

Unified, Elementary, and Secondary School Districts

Format table:

These codes were added to the Census Bureau's TIGER system in the 1990s. These values are as of 1-1-2010 (i.e., as used in the geographic headers of the 2010 census summary files.) They are "LEA" codes as assigned by the National Center for Educational Statistics. There are three levels of districts, but not all three will be defined for a census block. In many/most states, not all three levels are used. In Missouri, for example, only Unified and Elementary are used, and they are mutually exclusive (i.e., they do not overlap). These are five-digit codes as established by the National Census for Education Statistics. They are unique within state.

We have added two items here called best school district and best school district type. The best district attempts to assign the most relevant of the potential three districts assigned to a block. It turns out that in Missouri and many other states, there are not really separate overlapping coverages for the three school levels (unified, elementary, and seconday). If a unified school district is defined for the block, then best school district is assigned the code for that unified district and best school district type is assigned a value of "U". If no unified district is assigned to the block, then if an elementary district is defined, then this elementary district code is assigned as the best school and best school type gets a value of "E". If only a secondary district is assigned, then it becomes the best school and "S" is assigned as best school type.

We have both the original 2010 school district codes, as well as a set based on the codes for 2014, taken from the TIGER line faces files.

County Size

Counties are categorized by nine population interval categories. Even though we use the original name from the geographic headers portions of the census summary files where it is stored as a code, the values stored in MABLE (cntysc) are just character strings indicating the interval. The values are:

Place Size

Same idea as above, but this is for place size (placesc) rather than county.

Based on census 2000 place boundary definitions and populations.

Within a Place

This is a category variable that allows you to look at a breakout of an area based on how much of it is inside or outside of a place, with detail as to whether the place is incorporated or a Census Designated Place (CDP). The one-character code values are:

  1. Within an incorporated place
  2. Within a CDP
  3. Not in a place

Based on census 2010 place boundary definitions.

Census Place code

The Census Bureau has their own set of four-digit place codes that were used before they switched to five-digit FIPS codes some time between the 1980 and 1990 censuses. This field is blank for places that did not exist in 1980. Only useful for capturing codes that you plan to use in conjunction with earlier census data (1980 or earlier). Normally you will use the regular place geocode, which is the FIPS version.

Census County Subdivision code

This does for county subdivisions what the previous entry does for places. These are three-digit codes that the Census Bureau assigned and used in their products before switching to the more standard FIPS codes. These codes are only unique within county. They have leading zeroes and usually appear in increments of five. So most counties have CenCouSub codes of 005, 010, 015, etc.

Hospital Service Areas

Hospital Service Areas (HSAs) were created through The Dartmouth Atlas of Health Care many years ago using ZIP Code boundaries (not to be confused with ZCTA boundaries). ZIP Code boundaries and the Census geographic units in MABLE do not share a geographic hierarchy, so they do not link together without overlap between the geographies. HSAs are nested within HRRs.

A base crosswalk file was created for MABLE between 2010 Census Blocks (using internal points) and HSAs, using point-in-polygpon GIS processing allowing HSAs to be added to the MABLE database.

For more information on the creation of HSAs see For questions about HSA data, contact Nancy Marth at the Dartmouth Institute For Health Policy and Clinical Practice.

Hospital Referral Regions

These regions are closely related to the HSA geographies described just above. The methodology for creating them, contact information, etc. are the same. HSAs nest within these referral regions.

Additional Information

For additional background information on any of the geographic units maintained or utilized by the Census Bureau, you can view the Geographic Areas Reference Manual, which is now available on the Geography Divsion's home page.

Other useful links: