The composition of a population affords insight not only into present conditions within the population, but also into the potential for change in the future. The age-sex composition of a population can be represented graphically through a population pyramid, which shows the percent of total population in each age and sex cohort. Pyramids are commonly used to illustrate the populations of countries at different stages of both economic and demographic development. Inferences can be made about future growth potential due to population momentum and economic conditions associated with a high dependency ratio resulting from the large population under the age of 15 years. In contrast, the almost column-like pyramid of Spain reflects this country s more stable demographic situation.
Pyramids also reflect the demographic history of a country.
A pyramid for Germany would reveal the ravages of two world wars, as well as that country s post-war baby boom. At a different scale, comparison of pyramids for various states, Florida and Utah for example, reveals graphically just how diverse the U.S. population really is. Florida s median age of 37.6 years becomes quickly apparent when the state s pyramid is compared to that of Utah where the median age is only 26.8 years. Even a more local scale, pyramids tell an interesting story. For example, pyramids representing a transect from the central city into the distant rural-fringe suburbs traces the changing demographics a metropolitan area.