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Geography Identifiers

AFF specifies geographies by both name and by AFF geography identifiers. An AFF geography identifier is a combination of geographic codes that uniquely represent a geography.

The expectation is that applications use AFF-WS search services to search and discover geographies and their associated identifiers; expansion of search services capabilities are planned for future AFF-WS releases. It is NOT expected for consuming applications to build geographic identifiers on the fly, as this may lead to incorrect or inexistent geography, deviating from the end user's intent.

Geography Overview

This diagram shows the many geographic types for which data are available from the U.S. Census Bureau.

diagram of census geography hierarchy

With connecting lines, the diagram shows the hierarchical relationships between geographic types. For example, a line extends from states to counties because a state is comprised of many counties, and a single county can never cross a state boundary.

If no line joins two geographic types, then an absolute and predictable relationship does not exist between them.

For example, many places are confined to one county. However, some places extend over more than one county, such as New York City. Therefore, an absolute hierarchical relationship does not exist between counties and places, and any tabulation involving both these geographic types may represent only a part of one county or one place.

Because answers to many questions require parts of geographic types in relationship to other geographic types, the Census Bureau tabulates intersections of the basic geographic types by the selection sequence. Some examples:

  • A County planner would be interested in information about the Places (or parts of Places) within the County.

  • A Place planner would be interested in information about the Counties (or parts of Counties) within the Place.

There are over 200 selection sequences; each sequence is called a summary level and the collection of summary levels available for a dataset is the dataset's summary level sequence chart.

No dataset has data for all summary levels; see the dataset-specific technical documents for which datasets support which summary levels. The technical documents are available from American Factfinder and census.gov.

The relationships between summary levels and datasets can also be discovered interactively using American FactFinder's Advanced Search.

Notice that many lines radiate from blocks, indicating that most geographic types can be described as a collection of blocks, the smallest geographic unit for which the Census Bureau reports data.

Individual Geography Identifiers

A geography identifer that represents a single geography is a combination of geographic codes that uniquely represent a geography.

The basic format of an AFF single geography identifer is:

<<summmary-level-code>> + <<variant-code>> + <<component-code>> + "US" + <<sequence-of-codes>>

Where:

  • summary-level-code identifies the geographic summary level; a String[3] value. Popular summary levels include:
    010 = United States
    020 = Region
    030 = Division
    040 = State
    050 = ..... County
    060 = ..... ..... County Subdivision
    140 = ..... ..... Census Tract
    150 = ..... ..... ..... Block Group
    100 = ..... ..... ..... ..... Block [3]
    902 = ..... Equal Employment Opportunity County Set
    160 = ..... Place
    162 = ..... Estimates Universe Place
    E60 = ..... Economic Place 1
    E65 = ..... ..... County (or part)
    170 = ..... Consolidated City
    172 = ..... ..... Place within Consolidated City
    500 = ..... Congressional District 2
    610 = ..... State Legislative Districts, Upper Chamber [2]
    620 = ..... State Legislative Districts, Lower Chamber [2]
    950 = ..... School District (Elementary)/Remainder
    960 = ..... School District (Secondary)/Remainder
    970 = ..... School District (Unified)/Remainder
    320 = ..... Metropolitan Statistical Area/Micropolitan Statistical Area (or part)
    321 = ..... ..... Principal City (or part)
    E32 = ..... Area Outside of Metropolitan Statistical Area/Micropolitan Statistical Area (or part)
    340 = ..... Combined Statistical Area (or part)
    360 = ..... New England City and Town Area (or part)
    860 = ..... 5-Digit ZIP Code Tabulation Area
    861 = ..... 5-Digit ZIP Code
    E33 = ..... Commodity Flow Survey Area/Remainder
    250 = American Indian Area/Alaska Native Area/Hawaiian Home Land
    310 = Metropolitan Statistical Area/Micropolitan Statistical Area
    311 = ..... State (or part)
    312 = ..... ..... Principal City (or part)
    330 = Combined Statistical Area
    400 = Urban Area [2]
    904 = Puerto Rico Planning Region
    906 = American Housing Survey Area
    E20 = Commercial Region

Notes: 1 Economic Places are for economic datasets and are defined as Places plus County Subdivisions in States with strong Minor Civil Divisions (MCDs) 2 This geography type has variant-codes 3 Blocks are disseminated only for the Decennial Census

  • variant-code identifies the geographic variant, if any; a String[2] value.
    When more than one set of boundary definitions can exist for a given summary level in a given year or overlapping range of years, a variant-code extends the summary-level-code to allow distinct geography identifiers for all versions/vintages of geographies within a specific year. Variant-code examples:

    00 = the non-variant geography (the typical value for most geographies) 06 = 106th Congress 08 = 108th Congress ... 11 = 111th Congress 12 = 112th Congress 13 = 113th Congress ... 49 = 149th Congress C0 = Urban Area - 2000 C1 = Urban Area - 2010 L0 = State Legislative Districts, Lower Chamber - 2000 L1 = State Legislative Districts, Lower Chamber - Pre-2010 L2 = State Legislative Districts, Lower Chamber - 2010 U0 = State Legislative Districts, Upper Chamber - 2000 U1 = State Legislative Districts, Upper Chamber - Pre-2010 U2 = State Legislative Districts, Upper Chamber - 2010

  • component-code identifies the geographic component, if any; a String[2] value. A geographic component is a portion of a geography that meets a criteria such as Urban or Rural. Component availability varies by dataset and summary-level-code; typically components are available for summary-level-codes associated with large geographic areas such as Nation, Region, Division, State, and Congressional District. Component-code examples:

    00 = Not a geographic component (always available) 01 = Urban 43 = Rural A0 = In metropolitan or micropolitan statistical area C0 = In metropolitan statistical area E0 = In micropolitan statistical area G0 = Not in metropolitan or micropolitan statistical area

  • sequence-of-codes is a combination of FIPS and other codes that varies by summary-level-code.

The G001 table in most datasets provides the geographic identifiers for the dataset.

Summary level coverage by varies by dataset so different geographic identifiers may needed to access data in different datasets (see examples below).

The community facts geographic search provides simple geographic bridging for the most popular summary levels.

Be aware that data for all summary levels are not published every year; for example Block summary level data is only published every ten (10) years in the Decennial Census.

Geography Collection Identifiers

A geography identifer that represents a collection of geographies is a summary level in combination with a containing individual geography identifier. For example: "All States in the United States" or "All Counties in Florida".

The basic format of an AFF geography collection identifer is:

<<geography-identifier>> + "." + <<summary-level-code>> + <<variant-code>> + [ "." + <<full-or-partial-ind>> | <<filter-code>> ]

Where:

  • geography-identifier identifies the containing geography; a String value.

  • summary-level-code identifies the summary level of the collection; a String[3] value.

  • variant-code identifies the geographic variant of the collection; a String[2] value.

  • full-or-partial-ind identifies whether non-nested geographies are fully-nested (F) or fully-or-partially-nested (P) within the containing geography.

  • filter-code identifies that only a subset of the parent-child relationship is returned; not all collections support a filter code:

    • no filter = complete set of children returned
    • 001 = All States, District of Columbia, Puerto Rico, and the Island Areas within the United States
    • 001 = All Metropolitan Statistical Areas within the United States and Puerto Rico
    • 002 = All Micropolitan Statistical Areas within the United States and Puerto Rico
    • 003 = All [children] within [parent] for parents within the United States
    • 004 = All [children] within [parent] for parents within the United States and Puerto Rico
    • 005 = All Metropolitan Statistical Areas within the United States
    • 006 = All Micropolitan Statistical Areas within the United States

Only a limited set of geography collection identifiers are available.

The geographies found by the expansion of a geographic collection will vary by dataset due to U.S. Code Title 13 and statistical quality of the data. For example, for the American Community Survey in 2011 the collection "All Places in Virginia" returns only 14 geographies for the 1-Year Estimates dataset but returns 582 geographies for the 5-Year Estimates dataset.

Examples

Sample individual geographic identifiers:

0100000US            = United States
0100001US            = United States -- Urban
0400000US51          = Virginia
0500000US51059       = Fairfax County, Virginia
0600000US5105995847  = Springfield district, Fairfax County, Virginia
1400000US51059492000 = Census Tract 4920, Fairfax County, Virginia
1600000US5126592     = Fairfax Station CDP, Virginia
5001200US5111        = Congressional District 11 (112th Congress), Virginia
610U200US51039       = State Senate District 39 (2010), Virginia
620L200US51040       = State House District 40 (2010), Virginia
8600000US22039       = ZCTA5 22039

Sample geographic collection identifiers:

0100000US.04000      = All States within the United States and Puerto Rico
0100000US.04000.001  = All States within the United States, Puerto Rico, and the Island Areas
0100000US.05000.003  = All Counties within the United States
0100000US.05000.004  = All Counties within the United States and Puerto Rico
0400000US51.05000    = All Counties in Virginia
5001200US5101.05000P = All Counties fully within/partially within Congressional District 1 (112th Congress), Virginia

A given physical geography has a unique AFF geography identifier per summary level because the identifier reflects the summary level:

0500000US24510      = Baltimore city, Maryland (the County)
1600000US2404000    = Baltimore city, Maryland (the Place within State)
E600000US2451004000 = Baltimore city, Maryland (the Economic Place within State)


Last updated: August 02, 2017