In a population pyramid, the size of the population under investigation is depicted on the horizontal axis, and age is aligned on the vertical axis. The result is a series of bars stacked on top of one another, each representing an age category (typically in 5-year age groups), with the youngest age group represented by the bottom bar and the oldest age group by the uppermost bar. The horizontal length of each bar represents the number of individuals in the specific age group for the population depicted.
