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Federal Register / Vol. 86, No. 32 / Friday, February 19, 2021 / Notices
on data either from or contemporary with the decennial census, but were split based on the results of the previous decades data and delineation.
For the 2020 Census, the Census Bureau proposes using worker flow data i.e., commuting flows from the Longitudinal Employer-Household Dynamics LEHD Program to identify whether the agglomeration represents a single functionally integrated region or whether commuting patterns indicate the presence of distinct urban areas within the larger agglomeration. The LEHD worker flow data would be used in two stages. The first stage is an analysis of adjacent 2010 Census urban areas, based on aggregate commuter flows into and out of each urban area.
Adjacent 2010 Census urban areas will be merged if 50 percent or more of the workers in the smaller urban area are working in the larger urban area and 50
percent or more of the jobs in the smaller urban area are filled by workers residing in the larger urban area. If not merged, urban areas are selected for further analysis and split boundary adjustment. The second stage is identification of where to split large agglomerations, based on patterns observed by performing community detection on the LEHD worker flow data. Community boundaries resulting from application of the Leiden Algorithm 2 to the worker flow data will be used to adjust 2010 Census urban area split boundaries for the final 2020
Census urban areas. Application of this criterion could shift territory from one 2010 urban area to a different 2020
urban area. The resulting splits will reflect contemporaneous commuting patterns, which in turn, serve as proxy measures for other kinds of economic and social interactions within urban areas.

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3 Proposed Urban Area Criteria for the 2020 Census The proposed criteria outlined herein apply to the United States,3 Puerto Rico, and the Island Areas of American Samoa, the Commonwealth of the Northern Mariana Islands, Guam, and the U.S. Virgin Islands. The Census Bureau proposes the following criteria and characteristics for use in identifying the areas that will qualify for designation as urban areas for use in 2 Thomas, I., A. Adam, and A. Verhetsel.
Migration and commuting interactions fields: A
new geography with community detection algorithm? 2017. Belgeo. Online, 4. http
journals.openedition.org/belgeo/20507. Traag V.A, L. Waltman and N.J. van Eck. From Louvain to Leiden: Guaranteeing well-connected communities.
2019. Scientific Reports. 9:5233.
3 For Census Bureau purposes, the United States includes the 50 States and the District of Columbia.

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tabulating data from the 2020 Census, the American Community Survey ACS, the Puerto Rico Community Survey, and potentially other Census Bureau censuses and surveys.
A. 2020 Census Urban Area Definitions For the 2020 Census, an urban area will comprise a densely developed core of census blocks 4 that meet minimum housing unit density requirements, along with adjacent territory containing non-residential urban land uses as well as other lower density territory included to link outlying densely settled territory with the densely settled core. To qualify as an urban area, the territory identified according to the proposed criteria must encompass at least 4,000 housing units or at least 10,000 persons. The term rural encompasses all population, housing, and territory not included within an urban area.
As a result of the urban area delineation process, an incorporated place or census designated place CDP
may be partly inside and partly outside an urban area. Any census geographic areas, with the exception of census blocks, may be partly within and partly outside an urban area.
All proposed criteria based on land area, housing unit density, and population, reflect the information contained in the Census Bureaus Master Address File/Topologically Integrated Geographic Encoding and Referencing MAF/TIGER Database MTDB at the time of the initial delineation. All calculations of housing unit density include only land; the areas of water contained within census blocks are not used in density calculations.
Housing unit, population, and worker flow data used in the urban area delineation process will be those published by the Census Bureau for all public and official uses.
B. Proposed Urban Area Delineation Criteria The Census Bureau proposes to define urban areas primarily on the basis of housing unit density measured at the census block level of geography. The 385 housing units per square mile density threshold utilized in the delineation of urban areas is consistent with the 1,000 persons per square mile density used in the past, based on the 2019 ACS 1-year data average of an 4 A census block is the smallest geographic area for which the Census Bureau tabulates data and is an area normally bounded by visible features, such as streets, rivers or streams, shorelines, and railroads, and by nonvisible features, such as the boundary of an incorporated place, minor civil division, county, or other 2020 Census tabulation entity.

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estimated 2.6 persons per household for the United States.
1. Identification of Initial Urban Area Cores The Census Bureau proposes to begin the delineation process by identifying and aggregating contiguous census blocks each having a housing unit density of at least 385 housing units per square mile. This aggregation of continuous census blocks would be known as the initial urban area core.
The initial urban area core must encompass at least 385 housing units consistent with the requirement for at least 1,000 people in the 2010 criteria.
After the initial urban area core is identified, additional census blocks would be included if it is adjacent to other qualifying territory and if it meets any of the following criteria:
a. It has a housing unit density of at least 385 housing units per square mile.
b. At least one-third of the census block consists of territory with a level of imperviousness of at least twenty percent,5 and is compact in nature as defined by a shape index. A census block is considered compact when the shape index is at least 0.185 using the following formula: I = 4pA/P2 where I is the shape index, A is the area of the entity, and P is the perimeter of the entity.
c. At least one-third of the census block consists of territory with a level of imperviousness of at least twenty percent, and at least forty percent of its boundary is contiguous with qualifying territory.
The Census Bureau would apply proposed criteria 1.a, 1.b, and 1.c above until there are no blocks to add to the urban area. Any holes or remaining nonqualifying territory completely contained within an initial urban area core that is less than five square miles in area will qualify as urban via the criteria for inclusion of enclaves, as set forth below in the III. B. 5., subheading entitled, 5. Inclusion of Enclaves.
2. Inclusion of Group Quarters Census blocks containing institutional and non-institutional group quarters that are adjacent to census blocks qualifying based on the criteria outlined in step 1 above 1. Identification of Initial Urban Area Cores will be included in the urban area. This criterion accounts for the fact that group quarters, such as college dormitories, are not considered housing units by the 5 The Census Bureau has found in testing the NLCD that territory with an impervious percent less than twenty percent results in the inclusion of road and structure edges, and not the actual roads or buildings themselves.

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