A population pyramid or "age-sex pyramid" is a graphical illustration of the distribution of a population by age groups and sex; it typically takes the shape of a pyramid when the population is growing. Males are usually shown on the left and females on the right, and they may be measured in absolute numbers or as a percentage of the total population. The pyramid can be used to visualize the age of a particular population. It is also used in ecology to determine the overall age distribution of a population; an indication of the reproductive capabilities and likelihood of the continuation of a species. Number of people per unit area of land is called population density.
Nearly half of Libya's 2011 population consists of people younger than age 20.
Population density is a measurement of population per unit land area. It is mostly applied to humans, but sometimes to other living organisms too. It is a key geographical term.
Mongolian Steppes. Mongolia is the least densely populated country in the world due to its harsh climate as a result of its geography.
Monaco is currently the most densely populated nation in Europe.