1. Human Population Pyramids
Population pyramids are used by demographers as a tool for understanding the make-up of a given population, whether a city, country, region, or the world. 

2. A Population Pyramid is a graph that shows the age-sex distribution of a given population. It a graphic profile of the population’s residents. Sex is shown on the left/right sides, age on the y-axis, and the percentage of population on the x-axis. Each grouping (ex: males aged 0-4) is called a cohort.
world from 2010 

3. A population pyramid does not tell you the actual population in numbers. Rather, it displays percentages and shows what portion of people fall into each cohort. Demographers use population pyramids to see population trends in the past, examine the current resident profile, and also to project how the population will increase/decrease in the future.

4. Economic variations (such as a depression or job growth)
What determines the shape of a population pyramid?
Events that took place during the 70 – 80 years depicted in the graph all have the potential to impact the graph’s shape.
Economic variations (such as a depression or job growth)
Political changes (such as a new policy on family planning or a new tax break on dependents)
Conflicts (such as wars)
Public health trends and natural events (such as long-term droughts or an earthquake)
These things can impact birth and/or death rates. These, in turn, influence the shape of the population pyramid.

5. China’s pyramid from 2008 that is shown here
China’s pyramid from 2008 that is shown here. Where the graph shrinks in for the age cohorts around 50, this shows the slowing of population growth during the Great Chinese famine. After the famine, we see population started increasing again. But then, about 30 years ago, the pyramid starts becoming thinner again and this coincides with the institution of the “one child policy” that was put into law in The slight bulge in the cohort is a reflection of the larger bulge at (the lower bulge represents the children of the upper).

6. The Three Basic Shapes of Population Pyramids
Expansive Constrictive Stationary

7. Expansive population pyramids are used to describe populations that are young and growing. They are often characterized by their typical ‘pyramid’ shape, which has a broad base and narrow top. A larger percentage of the population in the younger age cohorts, usually with each age cohort smaller in size than the one below it. These types of populations are typically representative of developing nations, whose populations often have high fertility rates and lower than average life expectancies.  

8. Constrictive population pyramids are used to describe populations that are elderly and shrinking. Constrictive pyramids can often look like beehives and typically have an inverted shape with the graph tapering in at the bottom. Constrictive pyramids have smaller percentages of people in the younger age cohorts and are typically characteristic of countries with higher levels of social and economic development, where access to quality education and health care is available to a large portion of the population.

9. Stationary, or near stationary, population pyramids are used to describe populations that are not growing. They are characterized by their rectangular shape, displaying somewhat equal percentages across age cohorts that taper off toward the top. These pyramids are often characteristic of developed nations, where birth rates are low and overall quality of life is high.

10. Fertility Rate: The Average Number of children a woman will have in her lifetime Life Expectancy: The average number of years a person born today could expect to live under current death rates. Your own life expectancy changes as you grow older, and as you face different risks

11. Birth Rate: Annual Births per 1000 Death Rate: Annual Deaths per 1000

12. Demographic Transition Model
Stage 1: High Fluctuating. Birth and Death Rate are BOTH very HIGH Stage 2: Early Expanding. Birth rate remains high Death rate is falling. Population steadily Rises Stage 3: Late Expanding. Birth rate begins to fall Death rate continues to fall. Population is still Rising Stage 4: Low Stationary. Both Birth and Death rate are low. Population in now beginning to steady or plateau Stage 5: Low Declining: Birth rate falls below Death rate. Population begins to decrease