Population growth: In 1850 there were just 1 billion people on earth, now there are over 6 billion. More than 1 billion live in China; India hit 1 billion (and counting) in May, 2000.

Image of Seoul, Korea from an aerial view.

Source: seoul downtown2, Tim Palone, Pics4Learning

Understanding population is important for many reasons. In this lesson, you will discover some of those lessons while leaning to use an important tool called a population pyramid.