The population structure of a country is how it is made up of people of different ages, and of males and females. The common method to show the structure is by a population pyramid. This diagram is made up by putting two bar graphs (one for male, one for female) side by side. From this you can read off what percentage of a population is of a certain gender and age range. In the example below 4% of the population are females aged between 25 and 29.
Population Structure - Developing Countries
This population pyramid is wide at the base, which means there are a large proportion of young people in the country. It tapers very quickly as you go up into the older age groups, and is narrow at the top. This shows that a very small proportion of people are elderly.
This shape of pyramid is typical of a developing country, such as Kenya or Vietnam.
Population Structure - Developed Countries
This shape is typical of a developed country. It is narrow at the base, wider in the middle, and stays quite wide until the very top, as there is a sizable percentage of older people. Note that there are more old women than men. Italy and Japan have population structures that are of this shape.