Population pyramids show the structure of a population by comparing relative numbers of people in different age groups. Population structures differ markedly between Less Economically Developed Countries LEDCs and More Economically Developed Countries MEDCs. Population pyramids are used by demographers as a tool for understanding the make-up of a given population, whether a city, country, region, or the world. A population pyramid does not tell you the actual population in numbers. Rather, it displays percentages and shows what portion of people fall into each cohort.