Age-Sex Pyramids and Population Pyramids

The Most Useful Graphs in Population Geography

The most important demographic characteristic of a population is its age-sex structure. Age-sex pyramids (also known as population pyramids) graphically display this information to improve understanding and ease of comparison. The population pyramid sometimes has a distinctive pyramid-like shape when displaying a growing population. 

How to Read an Age-Sex Pyramid Graph

An age-sex pyramid breaks down a country or location's population into male and female genders and age ranges. Usually you'll find the left side of the pyramid graphing the male population and the right side of the pyramid displaying female population.

Along the horizontal axis (x-axis) of a population pyramid, the graph displays population either as a total population of that age or a percentage of the population at that age. The center of the pyramid starts at zero population and extends out to the left for male and right for female in increasing size or proportion of the population. 

Along the vertical axis (y-axis), age-sex pyramids display five-year age increments, from birth at the bottom to old age at the top.

Some Graphs Actually Look Like a Pyramid

Generally, when a population is growing steadily, the longest bars of the graph will appear at the bottom of the pyramid and will generally decrease in length as the top of the pyramid is reached, indicating a large population of infants and children which declines toward the top of the pyramid due to the death rate.

Age-sex pyramids graphically display long-term trends in the birth and death rates but also reflect shorter term baby-booms, wars, and epidemics.

The Three Types of Population Pyramids

Rapid Growth

Afghanistan Age-Sex Pyramid
This age-sex pyramid for Afghanistan shows very rapid growth. Courtesy U.S. Census Bureau International Data Base

This age-sex pyramid of Afghanistan's population breakdown in 2015 represents a fast growth rate of 2.3 percent annually, which represents a population doubling time of about 30 years.

We can see the distinctive pyramid-like shape to this graph, which displays a high birth rate (Afghan women have on average 5.3 children, this is the total fertility rate) and a high death rate (life expectancy in Afghanistan from birth is only 50.9).

Slow Growth

U.S. Age-Sex Pyramid
This age-sex pyramid for the United States displays slow population growth. Courtesy U.S. Census Bureau International Data Base

In the United States, the population is growing at a very slow rate of about 0.8 percent annually, which represents a population doubling time of almost 90 years. This growth rate is reflected in the more square-like structure of the pyramid.

The total fertility rate in the United States in 2015 is estimated at 2.0, which results in a natural decline in the population (a total fertility rate of about 2.1 is required for population stability). As of 2015, the only growth the United States is from immigration.

On this age-sex pyramid you can see that the numbers of people in their 20s of both genders is significantly higher than the number of infants and children aged 0-9. 

Also note the lump in the pyramid between the ages of about 50-59, this large segment of the population is the post-World War II Baby Boom. As this population ages and climbs up the pyramid, there will be a much greater demand for medical and other geriatric services but with fewer young people to provide care and support for the aging Baby Boom generation.

Unlike the Afghanistan age-sex pyramid, the United States population shows a significant number of residents aged 80 and above, showing that increased longevity is much more likely in the U.S. than in Afghanistan. Note the disparity between male and female elderly in the United States - women tend to outlive men in every population group. In the U.S. life expectancy for men is 77.3 but for women it is 82.1.

Negative Growth

Japan Age-Sex Pyramid
This age-sex pyramid for Japan shows negative population growth. Courtesy U.S. Census Bureau International Data Base.

 As of 2015, Japan is experiencing a negative population growth rate of -0.2%, forecast to drop to -0.4% by 2025.

Japan's total fertility rate is 1.4, far below the replacement rate necessary for a stable population of 2.1. As Japan's age-sex pyramid shows, the country has a huge number of elderly and middle-age adults (about 40% of Japan's population is expected to be over 65 by 2060) and the country is experiencing a dearth in the number of babies and children. In fact, Japan has experienced a record low number of births over the past four years.

Since 2005, Japan's population has been declining. In 2005 the population was 127.7 million and in 2015 the country's population dropped to 126.9 million. The Japanese population is projected to about 107 million by 2050. If current predictions hold true, by 2110, Japan is expected to have a population under 43 million people. 

Japan has been taking their demographic situation seriously but unless Japanese citizens start coupling and reproducing, the country will have a demographic emergency. 

U.S. Census Bureau International Data Base

The United States Census Bureau's International Data Base (linked in heading) can produce age-sex pyramids for nearly any country for a few years in the past and several years into the future. Select the "Population Pyramid Graph" option from the pull-down menu of options under the "Select Report" menu. The above age-sex pyramids were all created on the International Data Base site.