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# How to describe a population pyramid

If you've studied human geography at school or college it's likely you've come across population pyramids. These show an entire population -- usually that of a state or country -- subdivided by age into a bar chart. Population pyramids are likely to be hot topics in the news in coming years as ageing populations pose challenges for pension and service provisions in the future.

Look up and print three countries' population pyramids from the U.S. Census Bureau's International Database. On the data access page, select the name of the country you want, then select the most recent year available for that country. When you have the results, click on the tab labelled "Population Pyramid." Afghanistan, Japan and the United States are three good examples which illustrate how population pyramids work.

Look at one of the pyramids and ensure you understand the information it can give you. The pyramid is structured around an inverted "T" shape. The information to the right of the central vertical line refers to females within the population, while the information to the left represents males. Moving up the vertical line, you will be able to read the ages of the people represented, with the youngest at the bottom and the oldest at the top; the numbers along the bottom tell you how many people are in each age group.

Begin with the pyramid for Afghanistan. You should be able to see how it has a wide base, indicating a large number of children, but tapers as it rises through the age groups. This classic pyramid shape is what originally gave population pyramids their name and is typical of a developing country, where lots of children are born but death rates are high and few people live into very old age. Afghanistan's chart is described as an "expansive" pyramid.

Look at the pyramid for the United States. Note how the shape is much less triangular than that for Afghanistan. Instead of tapering as it moves up through the age groups, the sides of the pyramid are roughly straight, showing that more people are living into middle age and beyond. This is an example of a stable pyramid, typical of a developed country.

Look at the pyramid for Japan to see an example of a country now experiencing negative population growth. Note how the base of the pyramid, representing the number of children in the population, is narrower than the bars representing the middle-aged groups. The shape is now "top heavy." This shape of Japan's pyramid is described as "declining", a reference to the fact that it represents a population that is actually getting smaller over time.