Age structure

A population pyramid, also called an age pyramid or age picture is 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. This tool can be used to visualize sex and age composition of a particular population. It is also used in ecology to determine the overall age distribution of a population; an indication of the reproductive capabilities and likelihood of the continuation of a species.

Population pyramid often contains continuous stacked-histogram bars. The population size is depicted on the x-axis (horizontal), and age-groups on y-axis (vertical). Males are conventionally shown on the left and females on the right, and they may be measured by raw number or as a percentage of the total population.

Population pyramids are often viewed as the most effective way to graphically depict the age and sex distribution of a population, partly because of the very clear image these pyramids represent.

A great deal of information about the population broken down by age and sex can be read from a population pyramid, and this can shed light on the extent of development and other aspects of the population. A population pyramid also tells how many people of each age range live in the area. There tends to be more females than males in the older age groups, due to females' longer life expectancy.

Population pyramid gives a clear picture of how a country transitions from high fertility to low fertility rate. The population pyramid here indicates stage 3 on the demographic transition. The broad base of the pyramid means the majority of population lies between ages 0–14, which tells us that the fertility rate of the country is high and above population sub-replacement fertility level. There is a higher dependency ratio of younger population over the working population. Moreover, there is lesser older population due to shorter life expectancy which is around 60 years.

Each country will have different or unique population pyramids. However, most population pyramids will be defined as the following: Stationary, expansive, or constrictive. These types have been identified by the fertility and mortality rates of a country.

...
Wikipedia