A population pyramid is a type of bar graph used to show the age and gender structure of a country, city or other area. The horizontal axis is divided into either numbers or percentages of the population. The vertical axis shows age categories.
Stage 1 population pyramids:
- Wide base due to extremely high birth rate
- Infant and child mortality rates are high, so the sides of the pyramid curve in quickly
- Death rate is high in all age groups, so life expectancy is low
- Very narrow apex and the shortest of all the pyramids
Stage 2 population pyramids:
- Sides slightly less concave due to decrease in death rate
- Few more elderly people in population shown by apex
- Base narrower due to slight decrease in birth rate
Stage 3 population pyramids:
- Narrowing base shows decrease in birth rate
- Sides straighter as more people live into old age due to health improvements
Stage 4 population pyramids:
- Straight sides show steady birth rate
- Concave shape shows birth rate reducing
- Life expectancy high - most people die in old age
Stage 5 population pyramids:
- Increasing proportions in the very elderly group
- Middle aged generations much larger than those of children because of low birth rate
How can a population become sustainable?
A sustainable population is one whose growth and development is at a rate that does not threaten the success of future generations.
Most sustainable = stage 4 countries.
Why are stage 5 populations not sustainable?
Stage 5 populations are not sustainable because numbers are decreasing. If the population continues to decrease, the country will die out.
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