5. Population Pyramids

What are population pyramids?  What data do they show?

How can geographers use population pyramids to better under­stand the demographics of a country’s population?

What do population pyramids show us that we can’t see using other tools?

What do population pyramids look like in different stages of the demographic transition?

Definition of Population Pyramids:

• Population Pyramids are a display of a country’s population in groups of age and gender. A population pyramid normally shows the percentage of the total population in 5-year age groups, the youngest group being 0-4 years of age at the base of the pyramid and the oldest group near the top.
• The length of the bar represents the percentage of the total population contained in that group. Males are usually shown on the left side of the pyramid and females on the right.
• The shape of a pyramid is determined primarily by the CBR (Crude Birth Rate) in the community.

Understanding The Population Pyramid

• A significant amount 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 development of a country and other aspects of the population. A population pyramid also tells the council 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.
• The age structure of a population is extremely important in understanding similarities and differences among countries. The dependency ratio is the number of people who are too young or old to work, compared to those who are in their productive years.
• The number of males per hundred females in the population is the sex ratio.

Population Pyramids/ Demographic Transition

• A country in stage 2 (Developing) of the demographic transition, with a high CBR has a relatively large number of young children (the base of the pyramid is very wide). In stage 1 of the Demographic transition the CBR varied considerably from one year to the next; but in the long term they were roughly comparable at very high levels, thus making the base of the pyramid very wide. No country is in stage 1 of the Demographic Transition any longer, every nation has moved on to at least stage 2. The gap between the CDR and CBR narrows in countries that are in the third stage of the Demographic Transition (ex. Chile). The population pyramid has more of a rectangular base and comes to a point at the top. In contrast a country in stage 4 (Developed) with a relatively large number of older people has a graph with a wider top that resembles more of a rectangle than a pyramid.
• Stage 3 Country: Chile