Population pyramid: The diagram designed to show the comparison of the human population by sex and age at a given instant time, consisting of a pair of the histograms, one for every sex, lay on their sides with the same base. The diagram is intended to give a quick overall comparison of age and sex structure of population. The population whose pyramid has a broad base and narrow apex has high fertility rate. Changing shape over time shows the changing composition of the population related with the changes in fertility and mortality at each age. The instance in Figure shows population pyramids for the men and women in Australia in the year 2002.