Population pyramid
graphical illustration showing distribution of age groups in a population / From Wikipedia, the free encyclopedia
A population pyramid is a graph. It has two back-to-back bars. These bars show the population in groups of ages, with woman in one side and man in the other side.
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/7/7e/Angola_population_pyramid_2005.png/320px-Angola_population_pyramid_2005.png)
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/3/34/China_population_pyramid_2005.png/320px-China_population_pyramid_2005.png)
The pyramids show the age distribution of the place, which can help in understanding and predicting the development of a country.
There are three types of population pyramids:
- Stationary pyramid shows a constant population, with equal birth rate and death rate
- Expansive pyramid shows a growing population
- Constrictive pyramid shows a shrinking population
In this type of graph, a wide base means a very high birth rate and a narrow base means a low birth rate.