Issues that can be observed when looking at the population pyramid of the UK include: the baby booms of previous generations; the aging society created by low birth rate and longer life expectancy; the increasing number of dependents on a relatively smaller working population.
This population pyramid is a good example of a contracting population pyramid. China has implemented successful population control policies which have lead to a decreasing population. China has benefitted over the last 30 years from a demographic dividend as the number of people entering the workforce has increased relative to the number of dependents.
This population pyramid is a typical expansive population pyramid. It indicates a rapidly expanding population. There is a youth bulge evident which means that there are large number of young people in society. If policies can be put into place for the economy to expand quickly enough providing jobs for all the new entrants to the workplace, the country will benefit from a demographic dividend.
A stationary population pyramid has a low birth rate and a low death rate. The population is stable over time. Indonesia's population pyramid is fast becoming stationary indicating that it will reach peak population in the next generation.
Here we can see how the population pyramid of a country has changed over time. In this case, the population of the US has gone from being expansionary to stable in 100 years.