Understanding Population Density

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Written by: Darryl Cohen

While the United States population density is about 90 people per square mile, most people live in cities, which have a much higher density. Even among cities, density values can vary considerably from one city to another.

Population density allows for broad comparison of settlement intensity across geographic areas. In the U.S., population density is typically expressed as the number of people per square mile of land area. The U.S. value is calculated by dividing the total U.S. population (316 million in 2013) by the total U.S. land area (3.5 million square miles).

In a broad sense, this number tells us how many people would live within one square mile if the U.S. population were evenly distributed across its land area. In reality, however, we know that population is not evenly distributed across space. People tend to cluster in cities, and those who live in rural areas are spread out across a much more sparsely populated landscape.

While the population density inside U.S. cities (about 1,600 people per square mile) is much greater than that of unincorporated areas (about 35 people per square mile), density levels still vary quite a bit from city to city, and even across different neighborhoods within a single city.

For example, New York City’s density value (almost 28,000 people per square mile) is notably higher than that of Los Angeles (about 8,300 people per square mile). Within New York City, we find that residential neighborhoods with high-rise apartments and condos are much more densely populated than neighborhoods that consist of detached, single-family housing units. The Co-op City neighborhood in the Bronx has density levels that are greater than 33,000 people per square mile. Its high-rise development pattern differs considerably from that of Staten Island, where the overall density is about 8,000 people per square mile

When comparing population density values for different geographic areas, then, it is helpful to keep in mind that the values are most useful for small areas, such as neighborhoods. For larger areas (especially at the state or country scale), overall population density values are less likely to provide a meaningful measure of the density levels at which people actually live, but can be useful for comparing settlement intensity across geographies of similar scale.

For more information on this topic, see the report, Population Trends in Incorporated Places: 2000 to 2013, as well as Patterns of Metropolitan and Micropolitan Population Change: 2000 to 2010.

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New Population Projections Account for Differences in Fertility of Native- and Foreign-Born Women

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By Sandra L. Colby and Jennifer M. Ortman

Last December, the U.S. Census Bureau released its latest series of national population projections, providing perspective on the future composition of the nation’s population. A new report released today explores these projections. It uses current data, along with past trends in fertility, mortality and international migration, to anticipate changes in the population in the years to come.

This series of projections is the first to distinguish between the fertility of native- and foreign-born women, which allows us to make separate assumptions about how the fertility of women in each of these groups will change over time. Incorporating different fertility rates for women based on their nativity, which are consistent with past and present trends in fertility, is intended to improve Census Bureau projections of both births and the population.

Researchers, policymakers, businesses and other government agencies use population projections and the components of change (births, deaths and net migration) for planning purposes. For example, projections of births are of potential interest to those associated with the child care industry, while projections of the population under age 18 can be used by those tasked with planning for future demands on the education system.

Here is a look at the fertility assumptions used to produce the projections:

The total fertility rate is a measure used by demographers to estimate the average number of children women would have by the end of their reproductive years, assuming that they bore children according to a given set of age-specific fertility rates (the number of births during a year to women in a particular age group).

In 2014, the fertility rate in the projections was 1.85 for the total population, but this number masks considerable variation in the rates of foreign- and native-born women (see table). In the United States, foreign-born women have historically had higher fertility rates when compared with native-born women. This is reflected in the fertility assumptions used to produce the national projections. For instance, the fertility rate for foreign-born women in 2014 was 2.59 compared with 1.71 for native-born women.


There is also variation in fertility rates by Hispanic origin. In 2014, the fertility rate for all Hispanic women in the projections was 2.13 compared with 1.78 for all non-Hispanics. Of all women, foreign-born Hispanic women were projected to have the highest fertility rate throughout the projections series, at 3.16 in 2014 and 2.58 in 2050.

Projected births are calculated by applying these fertility rates to the projected female population. The share of projected births for any group reflects both the fertility rate for that group and the size of the population to which the rates are applied. Although fertility rates are higher for foreign-born women, the number of births projected to occur is lower than the number to native-born women.

Foreign-born women are projected to represent a smaller share of the total female population in the ages 14 to 54. In addition, foreign-born Hispanic women are projected to have the highest fertility rates. However, they are projected to contribute only 13.5 million, or just under 9 percent, of all births between 2014 and 2050. The relatively small share of births to women in this group is because they represented only 7.8 percent of the total female population in the reproductive ages in 2014 and 6.8 percent in 2050. Even though each woman in this group is projected to have more children on average, the collective number of children born to the group is small.

Learn more about how the U.S. population is projected to change by viewing the 2014 national population projections at: www.census.gov/population/projections.


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Percentage of Children living in Owner-Occupied Homes Still Down From Prerecession Levels

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By Emily Schondelmyer, demographer

The Census Bureau released its annual “Families and Living Arrangements” table package today, finding that about 20 percent of the nation’s children are receiving food stamps. The economic well-being of households with children declined during the recession, evidenced by a 7 percentage point drop in homeownership in 2014 (from 68 percent in 2007 to 61 percent today) among households with children. Not only is homeownership a key asset and financial investment for many families, it also plays an important role in the stability of children’s lives.


Looking at the changes between 2007 and 2014 by family type, the data show that the percentage of children living in owned homes:

  • dropped 6 percentage points for those living in families with cohabiting parents;
  • dropped 5 percentage points for those living in families with married parents; and
  • dropped 6 percentage points for those living with a father only.

There was no statistical difference among children living with their mother only and among those living without a parent. For children living with their mother only, the smaller drop in homeownership may be because they were less likely to live in an owned home to begin with.

In general, while most children living in two-parent homes live in an owned home, there is a large difference between married-parent families and cohabiting-parent families. In 2014, three quarters of children with married parents lived in an owned home, compared with just one-third of children with cohabiting parents.

The majority of children who live with married parents, their father only, or with no parents (for example, they live with grandparents) are living in an owned home. In contrast, children living with parents who cohabit or with their mother only tend to live in a rented home.

RS2 RS3Emily Schondelmyer is a demographer in the Census Bureau’s Fertility and Family Statistics Branch.

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Statistical Definition of ‘Family’ Unchanged Since 1930

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By David Pemberton, historian

What is the Census Bureau’s definition of “family”?

Printed decennial census reports from 1930 to the present are consistent in their definition of “family.” The 2010 version states: “A family consists of a householder and one or more other people living in the same household who are related to the householder by birth, marriage or adoption.”

The 1930 version is strikingly similar: “Persons related in any way to the head of the family by blood, marriage or adoption are counted as members of the family.”

But prior to 1930, the definition of a family was quite different.

The 1920 version went like this: “The term ‘family’ as here used signifies a group of persons, whether related by blood or not, who live together as one household, usually sharing the same table. One person living alone is counted as a family, and, on the other hand, the occupants or inmates of a hotel or institution, however numerous, are treated as a single family.”

The 1900 Census announced: “The word family has a much wider application, as used for census purposes, than it has in ordinary speech. As a census term, it may stand for a group of individuals who occupy jointly a dwelling place or part of a dwelling place or for an individual living alone in any place of abode. All the occupants and employees of a hotel, if they regularly sleep there, make up a single family, because they occupy one dwelling place …”

The older definition is closer to the current use of the term “household.”

Enumerator instructions beginning in at least 1860 and extending at least through 1940 emphasize this older definition of family.

Here is an example from the 1860 instructions: “By the term ‘family’ is meant either one person living separately and alone in a house, or a part of a house, and providing for him or herself, or several persons living together in a house, or part of a house, upon one common means of support and separately from others in similar circumstances. A widow living alone and separately providing for herself, or 200 individuals living together and provided for by a common head, should each be numbered as one family.”

The 1870 instructions add the element of eating together as one defining element of a family: “Under whatever circumstances, and in whatever numbers, people live together under one roof, and are provided for at a common table, there is a family in the meaning of the law.”

By 1930, the concept of a “household” had become more important and by implication was separated from the term “family”: “A household for census purposes is a family or any other group of persons, whether or not related by blood or marriage, living together with common housekeeping arrangements in the same living quarters.”

In 1960, the concepts of household and family were even more clearly delineated: “A household consists of a group of people who sleep in the same dwelling unit and usually have common arrangements for the preparation and consumption of food. Most households consist of a related family group. In some cases, you may find three generations represented in one household. Some household members may have no family relationship to the central group — boarders and servants, for example — but they should be included with the household if they eat and sleep in the same dwelling unit.”

In summary, the definition of family before 1930 was more similar to today’s definition of household. However, since 1930, the definition of family has remained the same, and includes those who are related to the householder by birth, marriage, or adoption.

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A Change in Circumstances: Family and Household Transitions and Child Well-Being

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Written By: Lynda Laughlin

Change is inevitable, but how often things change can matter for the well-being of children. A new report, A Child’s Day: Living Arrangements, Nativity, and Family Transitions: 2011, uses multiyear data from the Survey of Income and Program Participation to understand how often children experience family and household transitions.

The new report examines three types of transitions that children potentially face. A family structure transition occurs if the child experienced a change in family structure due to a parent getting married, divorced or cohabiting with a new partner. An employment transition occurs if either parent in the household lost or gained a job. Lastly, a residential transition occurs if the child moved at any point.


Over half (56 percent) of children experienced at least one type of transition between 2008 and 2011. The most common type of transition that children experienced was a change in a parent’s employment status (32 percent). Family income was associated with the occurrence of a household or economic transition.

Children living in economically well-off families (300 percent of poverty or higher) were less likely to experience a family, residential or parental employment transition compared with children living in families with monthly incomes below the poverty threshold.

Changes in the home environment and economic resources often overlap. Figure 1  shows how often changes in family structure, residential location and parental employment coincided among children who had at least one transition between 2008 and 2011. Overall, 56 percent (38.2 million) of children experienced at least one transition.

Of the 12.4 million children who experienced a family structure transition, 4.8 million also experienced a parental employment transition (39 percent). Among children who moved(19.6 million), a higher proportion of children were more likely to have also experienced a parental employment transition (42 percent) than to have undergone a residential move and change in family structure (26 percent). Overall, 3 percent (2.3 million) of children encountered all three transitions at least once between 2008 and 2011.

Children living below poverty were more likely to have encountered all three transitions compared with children living at or above poverty (6 percent and 3 percent, respectively).

Instability is often linked to child outcomes and is examined in more detail in our new report: http://www.census.gov/content/dam/Census/library/publications/2014/demo/p70-139.pdf.

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