A population pyramid is a type of graph that is used to illustrate the distribution of a population. It is named a population pyramid because the results are often formed in the shape of a pyramid.
This graphical tool is used to visualize the age and sex of a population. The graph is formed using stacked-histogram bars to create a horizontal bar diagram. Across the horizontal access is the size of the population, white the vertical access represents age groups. Each age group is typically broken down into 5-year groups. The youngest group is featured at the bottom of the pyramid, with each bar representing an older group. The oldest group is located on the top bar. It’s also important to note that female populations are represented on either the right or left side of the vertical axis, while males are represented on the opposite side.
The horizontal bar for each age group represents the number of individuals who fall within that group. While most population pyramids represent age and sex, some graphs break this down further into characteristics including race, geographic location or marital status.
There are three main types of population pyramids. These types are identified by the fertility and mortality rates of a country or other region. The first type of pyramid is a “stationary” pyramid. As the name suggests, this indicates that the age and sex of a population remains constant. This occurs when there are equal birth and death rates.
The next type of population pyramid is an “expansive” pyramid. This is a very wide pyramid at the base, where the youngest age groups are located. This indicates that there is a high birth rate and low life expectation. This indicates a population that is growing quickly.
The final type of pyramid is a “constrictive” pyramid. These pyramids are narrower at the bottom. A country or region with this type of pyramid has a population that is generally older. These areas typically have longer life expectancy rates and a low death rate, as well as a low birth rate. The younger population is smaller in these countries. This is typically observed in developed countries that have access to health care and birth control and fewer negative environmental factors.