Demographics Comparison

Katelyn Copenhaver

Age Structure Diagram Definition:

A graphical illustration that shows the distribution of various age groups in a population (typically that of a country or region of the world), which forms the shape of a pyramid when the population is growing.

United States' Age Structure Diagram

This diagram shows a stable population in the United States.

India's Age Structure Diagram

This diagram shows that there will an ever-increasing amount of births in India, due to the increase in the younger population.

How and why their age structures differ:

Population Geographers typically construct a population age structure diagram by plotting the percentages of numbers of males and females in the total population in each of three age categories:

  • prereproductive (ages 0-14)

  • reproductive (ages 15-44)

  • postreproductive (ages 45 and up)

With age and gender distribution data from a certain population, it is easy to construct an age structure diagram. Once the diagram is constructed, you can clearly see if the population will grow, decline, or experience no noticeable change in its population numbers; for example, if the diagram shows a pyramidal shape, then one can expect a rapid rise in population. If the diagram shows a generally straight up and down shape except for the older age groups, a stable population is thus revealed. If the diagram shows a top-heavy shape, then a decline is forecast for that population.

The diagram for India shows the unmistakable pyramidal shape caused by ever-increasing number of births. If we showed Japan’s diagram, it would demonstrate the classic shape of a shrinking population. In it, you would note how prereproductive age groups (0 – 14 years) have smaller populations than the reproductive age groups (15 - 44 years). The United States shows a more stable population. Except for the post-reproductive groups (45+ years), the populations for the age groups extend generally the same lengths.

Factors that contribute to the difference from country to country include birth rate/death rate, immigration, and emigration. Any country with many people below 15 years old (represented by a wide based population structure diagram) has a powerful built-in momentum to increase its population size unless death rates rise sharply.

The number of births rises even if women have only one or two children because of the large number of girls who will be soon moving into their reproductive years. In 2002, 30% of the world's people were under 15 years old. These 1.9 billion people have moved move into their reproductive years. This powerful force for continued population growth, mostly in developing countries, could be slowed by an effective program to reduce birth rates or a sharp rise in death rates.


  1. What does it represent if an age structure diagram is pyramid shaped?
  2. Throughout the world, why do population growth rates differ from country to country?
  3. Can age structure diagrams help in predicting population trends of the future? How?


  1. An increase in birth rates.
  2. Every country has different death rates, birth rates, etc.
  3. Yes; they tell us whether a population is growing, stable, or declining.