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MODULE 8

Population Composition

LEARNING GOALS 8-1 Ho w do w e describe the age struc tur e
8-1 How do we describe the age structure

of a population?
of a population?
8-1 Describe the age structure of a population.
8-2 Identify major social generations in the Age Structure
United States.
8-3 Define the sex ratio of a population. The age structure of a population refers to the breakdown

8-4 Explain the uses of population pyramids. of a population into different age groups or cohorts. For
example, we may use three age groups: pre- reproductive
(0–14 years old), reproductive (15–49 years of age), and
post-reproductive (50 years and older), or we can divide
the population into five-year age groups (0–4 years,
Learning about a country or region’s popula-
tion size and distribution is often the first step
4–9, 10–14, 15–19, and so on). We usually describe the
in understanding its population patterns and pro- age structure using percentages, but absolute numbers
cesses. Geographers are also interested in population are fine, too. Thus, we can say that in 2017, (1) there
composition, or the makeup of the population by age, were 73.7 million children younger than age 18 in the
sex, ethnicity, race, income, education, and other char- United States, or (2) children under 18 accounted for
acteristics. A country’s age and sex structure affects its 22.6 percent of the U.S. population. The U.S. census is
rates of birth, death, and migration, which help geogra- an important source of such data.
phers forecast future population levels. In this Module, As Figure 8.1 shows, age structure varies consider-
we discuss several key concepts in population compo- ably among countries. Some countries have an over-
sition, including age structure, social generations, sex whelmingly young population due to their high birth
ratio, and population pyramids. Knowledge about these rates, which means that the proportions of the young
topics helps us understand important elements of soci- people are relatively high. In most of the countries in
ety, including labor supply, social tension, demand for Africa, as well as some countries in Latin America and
goods and services, and the need for public policy (laws tropical Asia, close to half the population is younger
and government programs). than 15 years old. In Niger, 49.3 percent of the popula-
tion is younger than 15, and in sub-Saharan Africa as
a whole, 41 percent. Other regions, generally those that
TERMS TO KNOW . . . industrialized early, have a large proportion of people in
population composition: The makeup of the popula- the over 15 to under 65 age bracket. A growing number
tion by age and sex as well as by ethnic, racial, income, of affluent countries have remarkably aged populations
and educational background because their birth rates are low and people live a long
age structure: Refers to the breakdown of a population life. In Germany, for example, 21 percent of the people
into different age groups or cohorts are over the traditional retirement age of 65. Many
other European countries are not far behind.

22 Unit 2 Population and Migration Patterns and Process
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