Population pyramids are also known as age/sex diagrams.  They're good ways to show the structure of a population. They reflect the past of the population, and they tend to condition its future. They tell us a lot about the population.
    
     The age-sex distribution of a population is an important feature to analyze if you wish to understand a country's demographic situation. These statistics give governments and others one of the tools they need to make informed decisions that will affect a country's lives and future.
  
     A handy way to illustrate the structure of a population is to graph the number of males & females for various age groupings. A horizontal bar graph with data for males on the left and females on the right is called a population pyramid. A population pyramid shows the percentage of males and females in 5 year age groups.