“Urban” and “rural” are terms that bring to mind specific kinds of landscapes—densely developed areas in the case of urban, and small towns, farms and open spaces in the case of rural. While we can all think of specific areas in each category, it’s important to have a consistent measure to define these areas in order to produce meaningful data. 

After each decennial census, the U.S. Census Bureau redefines both areas, providing an important baseline for analyzing the distribution and characteristics of urban and rural populations and economic activity. We periodically review the criteria defining urban and rural areas to make sure the distinctions continue to be relevant for analysis, planning and decision making. We do this by publishing Federal Register Notices – first to gather feedback and then to notify the public of the changes in criteria.

In this post, we discuss several key changes to the urban area criteria we have made by incorporating learnings from analysis of 2010 Census urban areas, changes in settlement patterns, and discussions with users of our urban and rural classification.

Following the 2010 Census, the Census Bureau defined two types of urban areas:

• Urbanized areas with a population of 50,000 or more.
• Urban clusters with at least 2,500 but fewer than 50,000 people.

Both areas were defined based on population density measured at the census tract and block levels. We used two population density thresholds in the delineation process: 1,000 people per square mile when delineating the initial urban core and then 500 people per square mile to finish out the delineation as we moved outward through suburban territory to the edge of the urban area.

In 2010, nearly 81% of the U.S. population was urban and approximately 19% was rural. When using the same definitions from 2010, the 2016-2020 American Community Survey (ACS) 5-year estimates show the same percentages at the national level. 

Table 1. Population in Urban and Rural Areas, 2010 Census and 2016-2020 ACS.

Sources: 2010 Census; 2016-2020 ACS 5-year data.

After the 2020 Census, there are three key changes to the Census Bureau’s urban area concept and criteria:

• We increased the minimum population threshold to qualify as urban from 2,500 to 5,000, and we added an alternative: instead of qualifying based on population size, areas can now qualify based on a minimum housing unit threshold.
• We now use housing unit density instead of population density.
• We no longer distinguish between different types of urban areas.

The first two changes reflect a general shift by the Census Bureau toward using housing units to measure urbanization and identify qualifying urban areas. Each of these criteria changes is described more below.

With the new criteria, to qualify as urban, an area must encompass at least 5,000 people or at least 2,000 housing units. The minimum number of people is an increase from the former threshold of 2,500 people, which had been used since 1910. We chose 2,000 housing units as the alternative threshold because it's consistent with the 5,000 people threshold. Specifically, if you multiple 2,000 by 2.5 (the nationwide average of people per housing unit) it also equals 5,000.

This “either/or” approach has two benefits:

• Areas, such as seasonal communities or second-home communities, that are densely developed but have a lower population on Census Day (April 1) can qualify as urban based on the number of housing units.
• Areas that have higher than average people per housing unit ratios can qualify based on population.

Although the federal government does not have a standard definition of urban or rural, the Census Bureau’s classification often provides a baseline set of areas. Previously, other federal agencies applied higher population thresholds that aligned with their specific program needs. The Census Bureau’s previous threshold of 2,500 people was the lowest in use and, over the years, data users and analysts have questioned the continued validity of the 2,500-person threshold and asked if the Census Bureau would consider an increase.

If we apply the new population threshold criteria to the same 2016-2020 ACS 5-year estimates used in Table 1 above, this change would mean approximately 1,000 areas would shift from urban to rural status. These areas contain an estimated 3.5 million people. Using the new criteria, there will be about a 1 percentage point change – a slight decrease in the urban population and a slight increase in the rural population.  

Table 2 applies the new minimum thresholds to the 2010 Census and 2016-2020 ACS 5-year estimates populations.

Table 2.  Population in Urban and Rural Areas, 2010 Census and 2016-2020 ACS, Applying 2020 Thresholds.

Source: 2010 Census; 2016-2020 ACS 5-year data.

The second change is that we’re defining urban areas based on housing unit density measured at the census block level, instead of population density. Housing density provides a more direct measure of the densely developed landscape. The number of individuals in housing units can change over time, but the presence of housing on the landscape remains more stable.

Three density thresholds are used in the delineation process:

• 425 housing units per square mile define the initial urban core.
• Then 200 units per square mile fill in the remainder of the urban area, which is similar to the 2000 and 2010 censuses.
• 1,275 housing units per square mile ensures each qualifying urban area contains at least one high density nucleus.

The use of housing unit density also provides the ability to update urban areas between censuses. This is especially important in faster growing areas of the nation. Population counts at the census block level are available only from the once-a-decade census, so when population density at the block level is the primary measure of urbanization, we are limited to delineating urban areas only once every 10 years. We can use data in our Master Address File, a continuously updated, nationwide file of addresses with associated status codes and geographic information, to update urbanization on a more frequent basis when housing unit density is used as the primary urbanization measure. We haven’t made specific plans to do so, but we now have the ability.

The third change was our decision to cease distinguishing between different types of urban areas based on size of population above or below 50,000 people. We no longer label areas as either urbanized areas or urban clusters. All areas, regardless of population size, are simply called “urban areas.”

When we consider economic data for urban areas on either side of the 50,000-person threshold – areas of 49,000 to 51,000 – we see similarities in terms of economic activity (Table 3). Looking at numbers of firms and retail sales, the 50,000-person threshold does not appear to be a significant divide. For example, as shown in Table 3 below, the Danville, VA., area had higher retail sales in 2012 than two of the three areas above 50,000—New Bern, NC, and Pascagoula, MS. Also, in terms of per capita retail sales, Roswell, NM, with a population just below 50,000, did not differ much from New Bern, which had a population just over 50,000 in 2020. This suggests that when analyzing urban areas, we should also consider the market region surrounding the area; that is, the economic reach of the urban area into the surrounding rural area and not limit our attention only to the urban area.

We will continue to publish population counts for urban areas. It will still be possible for data users and agencies to identify and distinguish areas based on various sizes of population. As we have stated previously, we are committed to working with stakeholders and agencies to promote understanding of our classification.

Table 3. Economic Data for Urban Areas with Populations Between 49,000 and 51,000

Source: 2010 Census; 2012 Survey of Business Owners; 2012 Economic Census
Note: Data for each urban area are based on the author’s aggregation of data for places located within the urban area (Economic Census data are not tabulated for urban areas). 

The Census Bureau will announce urban areas based on the 2020 Census by the end of the year.  Go to Urban and Rural for more information on this topic. To learn about the history of the Census Bureau’s urban-rural classification, go to “A Century of Delineating a Changing Landscape.”

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