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
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.
This diagram shows the many geographic types for which data are available
from the U.S. Census Bureau.
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.
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
The relationships between summary levels and datasets can also be
discovered interactively using American FactFinder's
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>>
- summary-level-code identifies the geographic summary level; a
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 
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 
620 = ..... State Legislative Districts, Lower Chamber 
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 
904 = Puerto Rico Planning Region
906 = American Housing Survey Area
E20 = Commercial Region
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
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.
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
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.
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>> ]
geography-identifier identifies the containing geography;
summary-level-code identifies the summary level of the collection;
variant-code identifies the geographic variant of the collection;
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.
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