E7-6467. Census Block Group Program for the 2010 Census-Proposed Criteria

AGENCY:

Bureau of the Census, Commerce.

ACTION:

Notice of proposed program revisions and request for comments.

SUMMARY:

Block groups are statistical geographic divisions of a census tract, defined for the tabulation and dissemination of decennial census data. Block groups also will be used to tabulate and publish estimates from the American Community Survey (ACS) ^[1] after 2010. Each block group comprises a reasonably compact and contiguous cluster of census blocks; up to nine block groups can be contained within a single census tract.

Most provisions of the block group criteria for the 2010 Census remain unchanged from those used in conjunction with Census 2000. However, based on consultation with data users and internal review, the Bureau of the Census (Census Bureau) is proposing the following changes for the 2010 Census: (1) Increasing the minimum population and housing unit counts for block groups; (2) using housing unit counts (as an alternative to population counts) in the delineation of block groups; (3) applying the same population and housing unit thresholds to all types of populated block groups in the United States,^[2] including block groups delineated on American Indian reservations and/or off-reservation trust lands,^[3] the Island Areas,^[4] and encompassing group quarters, military installations, and institutions; (4) allowing the delineation of block groups for large water bodies with areas of approximately 100 square miles or more and special land uses (e.g., large airports or public parks) with an official name; and (5) allowing for geographic frameworks of tribal block groups (separate from the standard block groups defined within counties and standard census tracts) to be defined within federally-recognized American Indian reservations and/or off-reservation trust lands.

In addition to the proposed criteria, this notice includes a description of the changes from the criteria used for Census 2000 and a list of definitions of key terms used in the criteria.

The Census Bureau is publishing this notice in the Federal Register to request comments from the public and other government agencies. The Census Bureau will respond to the comments received as part of the publication of final criteria in the Federal Register. After the final criteria are published in the Federal Register, the Census Bureau will offer designated governments or organizations an opportunity to review and, if necessary, suggest updates to the boundaries and attributes of the block groups in their geographic area under the Participant Statistical Areas Program (PSAP). In addition to block groups, the program also encompasses the review and update of census tracts, census designated places, and census county divisions.

DATES:

Written comments must be submitted on or before July 5, 2007.

ADDRESSES:

Please direct all written comments on this proposed program to the Director, U.S. Census Bureau, Room 8H001, Mail Stop 0100, Washington, DC 20233-0001.

FOR FURTHER INFORMATION CONTACT:

Requests for additional information on this proposed program should be directed to Michael Ratcliffe, Chief, Geographic Standards and Criteria Branch, Geography Division, U.S. Census Bureau, via e-mail at [e-mail] or telephone at 301-763-3056.

SUPPLEMENTARY INFORMATION:

I. History of Block Groups

The Census Bureau first delineated block groups as statistical geographic divisions of census tracts for the 1970 Census, comprising contiguous combinations of census blocks for data presentation purposes. At that time, census block groups only existed in urbanized areas in which census blocks were defined. Block groups were defined without regard to political and administrative boundaries, with an average population of 1,000, and to be approximately equal in area.

As census block, block group, and census tract data were used increasingly by data users, the Census Bureau expanded these programs to cover additional geographic areas, while redefining the population threshold criteria to more adequately suit data users' needs. The 1990 Census was the first in which census blocks and block groups were defined throughout the entirety of the United States, Puerto Rico, and the Island Areas. For Census 2000, as with census tracts, the Census Bureau increased the number of geographic areas whose boundaries could be used as block group boundaries, and allowed tribal governments of federally recognized American Indian tribes with a reservation and/or off-reservation trust lands to delineate block groups without regard to state and/or county boundaries, provided the tribe had a 1990 Census population of at least 1,000.

II. General Principles and Criteria for Block Groups for the 2010 Census

A. General Principles

1. Block groups are statistical geographic divisions of a census tract, defined by the Census Bureau in cooperation with local officials and organizations, for the tabulation and dissemination of decennial census data as well as period estimates of demographic and housing characteristics from the ACS.

2. Because block groups are used to present and analyze sample-based statistical data, the amount of population or housing units within a block group is an important consideration. As a general rule, estimates from programs providing sample data, including the ACS, for geographic areas with smaller populations are subject to higher variances than comparable estimates for areas with larger populations. Aiming to create block groups that fall between the minimum and maximum thresholds will improve the reliability and availability of data, and local governments and planners should consider these factors when defining their block groups.

3. Block groups form the geographic framework within which the Census Bureau defines census blocks for use in tabulating and presenting decennial census data. Census blocks are numbered within block groups.

4. Geographic areas that are not characterized by a residential population, such as parks, large industrial areas, and water bodies, and which local participants may wish to separate from populated census tracts for analytical or cartographic purposes, or both, may be identified as individual block groups.

B. Proposed Changes to the Block Group Criteria for the 2010 Census

Most provisions of the block group criteria for the 2010 Census would remain unchanged from those used in conjunction with Census 2000 with the following exceptions:

1. The Census Bureau proposes to increase the minimum population and housing unit counts for block groups to 1,200 and 480, respectively, to support block group sample data reliability and availability and to lower the variance of the sample data. The sample size for the ACS is smaller than the sample from the decennial census long form of previous censuses. As a general rule, estimates from programs providing sample data, including the ACS, for geographic areas with smaller populations will be subject to higher variances than comparable estimates for areas with larger populations. In addition, the Census Bureau's disclosure rules will have the effect of restricting the availability and amount of data for areas with small populations. Aiming to create block groups that fall between the minimum and maximum thresholds will improve the reliability and availability of data, and local governments and planners should consider these factors when defining their block groups.

2. Housing unit counts may be used instead of population counts in the delineation of block groups. This change seeks to accommodate seasonal communities in which residents may not be present on the date of the decennial census, but will be present at other times of the year and for which data may be reflected in the ACS.

3. For Census 2000, minimum population thresholds for block groups varied. The minimum population threshold for block groups delineated on American Indian reservations and off-reservation trust lands was 300. This differed from the minimum threshold of 600 people for block groups defined elsewhere in the United States, as well as in Puerto Rico and the Island Areas. The maximum population for a block group in any of these areas was 3,000. In addition, for Census 2000, block groups that enclosed an institution, a military installation, or other “special place” had a minimum population requirement of 300 inhabitants, with no optimum or maximum population.

For the 2010 Census, the same population and housing unit thresholds (minimum: 1,200 inhabitants or 480 housing units; maximum: 3,000 inhabitants or 1,200 housing units) would apply to all types of populated block groups, including block groups delineated for American Indian reservations and off-reservation trust lands, the Island Areas, and encompassing group quarters, military installations, and institutions. The Census Bureau proposes this change in order to aid in the availability and reliability of data for all block groups and to create a single national standard.

4. The delineation of block groups would be permitted, and encouraged, for the following specific types of geographic areas:

a. Large water bodies with areas of approximately 100 square miles or more.

b. Special land uses (e.g., large airports, public parks, or public forests) with an official name.

A single water body or special land use block group will be delineated to be coextensive with, or covering the same territory as, the water body or special land use tract in which it is located.

The Census Bureau would require that block groups delineated to encompass large water bodies and special land uses have little or no residential population. The Census Bureau recognizes that some special land use areas not generally intended for residential population, such as parks, may contain some population, such as caretakers or the homeless. Our intent is to allow for the delineation of parks and other special land use areas as separate block groups and, therefore, will accept such areas as block groups even if some residential population is present. All such block groups would meet all other block group criteria.

5. A geographic framework of tribal block groups, separate from the standard block groups defined within counties, may be defined within federally recognized American Indian reservations and/or off-reservation trust lands, subject to other population, housing, and boundary criteria contained in this document. This represents a change from the practice for Census 2000. The Census Bureau proposes this change to better recognize the unique statistical data needs of federally recognized American Indian tribes and their reservation and off-reservation trust lands.

C. Block Group Criteria for the 2010 Census

The criteria proposed herein apply to the United States, including federally recognized American Indian reservations and off-reservation trust lands, Puerto Rico, and the Island Areas. In accordance with the final criteria, the Census Bureau may modify and, if necessary, reject any proposals for block groups that do not meet the established criteria. In addition, the Census Bureau reserves the right to modify the boundaries and attributes of block groups as needed to meet the published criteria and/or maintain geographic relationships before the final tabulation geography is set for the 2010 Census.

The Census Bureau proposes the following criteria for use in delineating 2010 Census block groups.

1. A block group must comprise a reasonable compact, contiguous land area.

Noncontiguous boundaries are permitted only where a contiguous area or inaccessible area would not meet population or housing unit count requirements for a separate block group, in which case the noncontiguous or inaccessible area must be combined within an adjacent or proximate block group. For example, an island that does not meet the minimum population threshold for recognition as a separate block group should be combined with other proximate land to form a single block group. Each case will be reviewed and accepted at the Census Bureau's discretion.

2. Block groups must not cross census tract boundaries.

This criterion supersedes all population and housing unit requirements or guidelines. By extension, because census tracts cannot cross county and state boundaries, neither can block groups. It is only permissible to define a standard block group with less than 1,200 people in a county that has a population less than 1,200.

3. Block groups must cover the entire land and water area of each census tract.

Because census tracts must cover the entire area of a county, by definition block groups also must cover the entire area of each county. In counties containing coastal waters, territorial sea, and portions of the Great Lakes, and very large, contiguous, inland water bodies, a single water body tract and a coextensive block group should be created for each discrete water body to provide for complete census block group coverage.

4. Block group boundaries should follow visible and identifiable features.

To make the location of block group boundaries less ambiguous, wherever possible, block group boundaries should follow visible and identifiable features. The Census Bureau also permits the use of state and county boundaries in all states and incorporated place and minor civil division boundaries in states where those boundaries tend to remain unchanged over time (see Table 1). The use of visible features also makes it easier to locate and identify block group boundaries over time as the locations of many visible features in the landscape tend to change infrequently.

The following features are preferred as block group boundaries for the 2010 Census:

a. State, county, and census tract boundaries must always be block group boundaries. This criterion takes precedence over all other criteria or requirements.

b. American Indian reservation and off-reservation trust land boundaries.

c. Visible, perennial natural and cultural features, such as roads, shorelines, rivers, perennial streams and canals, railroad tracks, or above-ground high-tension power lines.

d. Boundaries of legal and administrative entities in selected states. Table 1 identifies by state which minor civil division (MCD) and incorporated place boundaries may be used as block group boundaries.

Table 1.—Acceptable MCD and Incorporated Place Boundaries

Boundaries	All MCD boundaries	Boundaries of MCDs not coincident with the boundaries of incorporated places that themselves are MCDs	All incorporated place boundaries	Only conjoint incorporated place boundaries
Alabama				X
Alaska				X
Arizona				X
Arkansas				X
California				X
Colorado				X
Connecticut	X		X
Delaware				X
Florida				X
Georgia				X
Hawaii				X
Idaho				X
Illinois		X a		X
Indiana	X			X
Iowa		X		X
Kansas		X		X
Kentucky				X
Louisiana				X
Maine	X		X
Maryland				X
Massachusetts	X		X
Michigan		X		X
Minnesota		X		X
Mississippi				X
Missouri		X b		X
Montana				X
Nebraska		X a		X
Nevada				X
New Hampshire	X		X
New Jersey	X		X
New Mexico				X
New York	X		X
North Carolina				X
North Dakota		X		X
Ohio		X		X
Oklahoma				X
Oregon				X
Pennsylvania	X		X
Rhode Island	X		X
South Carolina				X
South Dakota		X		X
Tennessee				X
Texas				X
Utah				X
Vermont	X		X
Virginia				X
Washington				X
West Virginia				X
Wisconsin		X		X
Wyoming				X
a Townships only.
b Governmental townships only.

e. Additionally, the following legally defined, administrative boundaries would be permitted as block group boundaries:

i. Barrio, barrio-pueblo, and subbarrio boundaries in Puerto Rico;

ii. Census subdistrict boundaries in the U.S. Virgin Islands;

iii. County and island boundaries (both MCD equivalents) in American Samoa;

iv. Election district boundaries in Guam;

v. Municipal district boundaries in the Commonwealth of the Northern Mariana Islands; and

vi. Alaska Native regional corporation boundaries in Alaska, at the discretion of the Census Bureau, insofar as such boundaries are unambiguous for allocating living quarters as part of 2010 Census activities.

f. When acceptable visible and governmental boundary features are not available for use as block group boundaries, the Census Bureau may, at its discretion, approve other nonstandard visible features, such as ridge lines, above-ground pipelines, intermittent streams, or fence lines. The Census Bureau may also accept, on a case-by-case basis, the boundaries of selected nonstandard and potentially nonvisible features, such as the boundaries of military installations, National Parks, National Monuments, National Forests, other types of parks or forests, airports, marine ports, cemeteries, golf courses, penitentiaries/prisons, glaciers, or the straight-line extensions of visible features and other lines-of-sight.

g. The boundaries of large water bodies and special land use tracts, including parks, forests, and military installations, provided the boundaries are clearly marked or easily recognized.

5. Population, Housing Unit, and Area Thresholds

The Census Bureau proposes the following population, housing unit, and area threshold criteria for census block group (as suggested in Table 2). Any block group that does not meet the minimum population or housing unit threshold must be revised.

Table 2.—Block Group Thresholds

Block group type	Threshold type	Minimum	Maximum
Standard & tribal block groups	Population threshold	1,200	3,000
	Housing Unit threshold	480	1,200.
Water body block groups	Area threshold (square miles)	100	none
Special land use block groups	Area threshold for an urban area (square miles)	1	none
	Area threshold outside an urban area (square miles)	10	none

a. Census 2000 population counts should be used in census block group review in most cases. Housing unit counts should be used for block groups in seasonal communities that have no or low population on census day (April 1). Locally produced population and housing unit estimates can be used when reviewing and updating block groups, especially in areas that have experienced considerable growth since Census 2000.

b. The housing unit thresholds are based on a national average of 2.5 persons per household. The Census Bureau recognizes that there are regional variations to this average, and will take this into consideration when reviewing all census block group proposals.

c. For the 2010 Census, the Census Bureau encourages the delineation of special use census tracts, hence special use block groups, in specific types of areas:

i. A special land use block group must be designated as a specific land use type (e.g. state park), must have an official name (e.g., Jay Cooke State Park), have little or no residential population, and must not create a noncontiguous block group. In some instances, multiple areas can be combined to form a single special land use block group if the land management characteristics are similar, such as a special land use block group comprising adjacent federal and state parks. If the special land use block group is delineated in a densely populated, urban area, the block group must have an area of approximately one square mile or more. If the special land use block group is delineated completely outside an urban area, the block group must have an area of approximately 10 square miles or more.

ii. A water body block group must encompass all or part of a territorial sea, coastal water, a Great Lake, or an inland water body at least 100 square miles in area. If an inland water body meets this criterion and is in more than one county, each county can delineate a block group for its portion of the water body. Any islands within a qualifying water body should be included within a separate block group.

6. Identification of Block Groups

a. A block group encompasses a cluster of census blocks. Each block group is identified using a single-digit number that will correspond to the first digit in the number of each block that comprises it. For example, census block group 3 includes all census blocks numbered in the 3000 range within a single census tract.

b. The range of acceptable block group numbers is 1 through 9. Block group numbers must always be unique within a census tract.

7. Block Group Types

Table 3.—Table 3 Below Contains a Summary of the Types of Block Groups (With Their Respective Population, Housing Unit and Area Characteristics) That the Census Bureau Proposes To Use for the 2010 Census. Summary of Block Group Types

	How distinct from standard block groups	Population thresholds	Housing unit thresholds	Area thresholds
Standard & tribal block groups	Tribal block groups are conceptually similar and equivalent to census block groups defined within the standard state-county-tract-block group geographic hierarchy used for tabulating and publishing statistical data	Minimum: 1,200; Maximum: 3,000	Minimum: 480; Maximum: 1,200	none.
Water body block groups	A block group coextensive with a water body tract, encompassing all or part of a territorial sea, coastal water, a Great Lake, or an inland water body at least 100 square miles area	Zero	Zero	100 square miles if an inland water body.
Special land use block groups	A block group coextensive with a special land use tract, encompassing a large airport, public park, or public forest with little or no population or housing units. In a densely populated, urban area, a special land use block group must be approximately one square mile in area or greater. If delineated completely outside an urban area, a special land use block group must have an area of ten square miles or greater	Little or none	Little or none	one square mile within an urban area/ten square miles outside an urban area.

D. Tribal Block Groups

Tribal block groups are statistical geographic entities defined by the Census Bureau in cooperation with tribal officials to provide meaningful, relevant, and reliable data for small geographic areas within the boundaries of federally recognized American Indian reservations and/or off-reservation trust lands. As such, they recognize the unique statistical data needs of federally recognized American Indian tribes. The delineation of tribal block groups allows for an unambiguous presentation of statistical data specific to a federally recognized reservation and/or off-reservation trust lands without the imposition of state or county boundaries, which might artificially separate American Indian populations located within a single reservation and/or off-reservation trust land. To this end, the American Indian tribal participant ^[5] may define tribal block groups that cross county or state boundaries, or both. Tribal block groups must be delineated to meet all other census block group criteria, and must be numbered uniquely so as to clearly distinguish them from county-based block groups. Tribal block group boundaries will be held as census block boundaries. Census blocks, however, will be numbered uniquely within county-based block groups. Tribal block groups are conceptually similar and equivalent to census block groups defined within the standard state-county-tract-block group geographic hierarchy used for tabulating and publishing statistical data.

In order to provide meaningful statistical geographic areas within the reservation and/or off-reservation trust land, as well as make meaningful and reliable data available for these areas and their populations, the Census Bureau proposes that for the 2010 Census, standard block groups be delineated nationwide, and the tribal block group geography be maintained separately, and defined through a separate program designed specifically for tribal statistical geography. This differs from the procedure for Census 2000 in which tribal block groups were defined for federally recognized American Indian reservations and/or off-reservation trust lands, and standard block groups were identified by superimposing county and state boundaries onto the tribal block groups.

For Census 2000 products in which data were presented by state and county, the standard state-county-census tract-block group hierarchy was maintained, even for territory contained within an American Indian reservation and/or off-reservation trust land. In such instances, the state/county portions of tribal block groups were identified as individual block groups, and these standard block groups may not have met the minimum population or housing unit thresholds, potentially limiting sample data reliability or availability for both the tribal block group and the derived standard block groups. The proposed change in the tribal block group program for the 2010 Census, creating standard block groups nationwide and maintaining tribal block groups as a completely separate set of geography from standard block groups in both geographic and data presentation purposes, seeks to eliminate, in part, these data issues from Census 2000.

As with standard block groups submitted through the program, the tribal block groups would be submitted to the Census Bureau, and would be subject to review to ensure compliance with the final published criteria. Tribal block groups will be defined as part of a separate Tribal Statistical Areas Program (TSAP) for the 2010 Census. Detailed criteria pertaining to tribal block groups will be published in a separate Federal Register notice pertaining to all American Indian statistical areas defined through the TSAP.

III. Definitions of Key Terms

Alaska Native regional corporation (ANRC)—A corporate geographic area established under the Alaska Native Claims Settlement Act (Pub. L. 92-203), to conduct both, the business and nonprofit affairs of Alaska Natives. Twelve ANRCs cover the entire State of Alaska except for the Annette Island Reserve.

American Indian off-reservation trust land (ORTL)—A federally recognized American Indian land area located outside the boundaries of an American Indian reservation whose boundaries are established by deed and over which a federally recognized American Indian tribal government has governmental authority.

American Indian reservation (AIR)—A federally recognized American Indian land area with boundaries established by final treaty, statute, executive order, and/or court order and over which a federally recognized American Indian tribal government has governmental authority. Along with reservation, designations such as colonies, communities, pueblos, rancherias, and reserves apply to AIRs.

Coastal water—Water bodies between territorial seas and inland water, the encompassing headlands being more than one mile apart and less than 24 miles apart.

Conjoint—A description of a boundary shared by two adjacent geographic entities.

Contiguous—A description of areas sharing common boundaries, such that the areas, when combined, form a single piece of territory. Noncontinuous areas form disjoint pieces.

Great Lakes' waters—Water area beyond one mile wide headland embayments located in any of the five Great Lakes: Erie, Huron, Michigan, Ontario, or Superior.

Group quarters (GQ)—A place where people live or stay, in a group living arrangement, that is owned or managed by an entity or organization providing housing and/or services for the residents. This is not a typical household-type living arrangement. These services may include custodial or medical care, as well as other types of assistance, and residency is commonly restricted to those receiving these services. People living in group quarters are usually not related to each other. Group quarters include such places as college residence halls, residential treatment centers, skilled nursing facilities, group homes, military barracks, correctional facilities, and workers' dormitories.

Incorporated place—A type of governmental unit, incorporated under state law as a city, town (except in New England, New York, and Wisconsin), borough (except in Alaska and New York), or village, generally to provide governmental services for a concentration of people within legally prescribed boundaries.

Inland water—Water bodies entirely surrounded by land or at the point where their opening to coastal waters, territorial seas, or the Great Lakes is less than one mile across.

Minor civil division (MCD)—The primary governmental or administrative division of a county in 28 states and the Island Areas having legal boundaries, names, and descriptions. MCDs represent many different types of legal entities with a wide variety of characteristics, powers, and functions depending on the state and type of MCD. In some states, some or all of the incorporated places also constitute MCDs.

Nonvisible feature—A map feature that is not visible on the ground, such as a city or county boundary through space, a property line, line-of-sight extension of a road.

Special land use block group—Block group delineated coextensive with, or covering the same area as, the special land use tract.

Special land use tract—Type of census tract that must be designated as a specific land use type (e.g. state park) and have an official name (e.g., Jay Cooke State Park), must have little or no residential population or housing units, and must not create a noncontiguous census tract. If delineated in a densely populated, urban area, a special land use tract must have an area of approximately one square mile or more. If delineated completely outside an urban area, a special land use tract must have an area of approximately 10 square miles or more.

Territorial seas—Water bodies not included under the definition for inland water, coastal water, or Great Lakes' waters, see above.

TIGER—Topologically Integrated Geographic Encoding and Referencing database developed by the Census Bureau to support its mapping needs for the Decennial Census and other Census Bureau programs. The topological structure of the TIGER database defines the location and relationship of boundaries, streets, rivers, railroads, and other features to each other and to the numerous geographic areas for which the Census Bureau tabulates data from its censuses and surveys.

Visible feature—A map feature that can be seen on the ground, such as a road, railroad track, major above-ground transmission line or pipeline, river or stream, shoreline, fence, sharply defined mountain ridge, or cliff. A nonstandard visible feature is a feature that may not be clearly defined on the ground (such as a ridge), may be seasonal (such as an intermittent stream), or may be relatively impermanent (such as a fence). The Census Bureau generally requests verification that nonstandard features used as boundaries for the PSAP geographic areas pose no problem in their location during field work.

Water body block group—Block group delineated coextensive with, or covering the same area as, the water body tract.

Water body tract—Type of census tract encompassing territorial seas, coastal water, the Great Lakes, or inland water at least 100 square miles in area. If an inland water body meets this criteria, each county can delineate a census tract for its portion of the water body.

Executive Order 12866

This notice has been determined to be not significant under Executive Order 12866.

Paperwork Reduction Act

This program notice does not represent a collection of information subject to the requirements of the Paperwork Reduction Act, 44 U.S.C. Chapter 35.

Dated: April 3, 2007.

Charles Louis Kincannon,

Director, Bureau of the Census.

Footnotes

1.  The ACS is conducted in the United States and in Puerto Rico. In Puerto Rico, the survey is called the Puerto Rico Community Survey. For ease of discussion, throughout this document the term ACS is used to represent both the survey that is conducted in the United States and in Puerto Rico.

2.  For Census Bureau purposes, the United States includes the fifty states and the District of Columbia.

3.  The proposed criteria for the tribal statistical areas program will be outlined in a separate Federal Register notice. In the tribal statistical areas program, federally recognized American Indian tribes that have a reservation and/or off-reservation trust land may delineate census designated places and, if these areas have a population of 2,400 or greater, may delineate tribal tracts and tribal block groups for their reservation and off-reservation trust land.

4.  For Census Bureau purposes, the Island Areas includes American Samoa, the Commonwealth of the Northern Mariana Islands, Guam, the U.S. Virgin Islands, and the U.S. Minor Outlying Islands. The U.S. Minor Outlying Islands is an aggregation of nine U.S. territories: Baker Island, Howland Island, Jarvis Island, Johnston Atoll, Kingman Reef, Midway Islands, Navassa Island, Palmyra Atoll, and Wake Island.

5.  For federally recognized American Indian tribes with reservations and/or off-reservation trust lands that have more than 2,400 residents, the Census Bureau will offer the tribal government the opportunity to delineate tribal block groups and other tribal statistical geography on their reservation and/or off-reservation trust land. For federally recognized tribes with an American Indian reservation and/or off-reservation trust land that have fewer than 2,400 residents, the Census Bureau will define one tribal tract and one tribal block group coextensive with the American Indian reservation and/or off-reservation trust land.