Maps showing the regional distribution and density of populations tell us about the number of people in coun- tries or regions, but they cannot reveal two other aspects of those populations: the number of men and women and their ages. These aspects of population, the population composition, are importants because a populous coun- try where half the population is very young has quite dif- ferent problems from a populous country where a large proportion of the population is elderly. When geogra- phers study populations, therefore, they are concerned not only with spatial distribution and growth rates but also with population composition.