It took me a few minutes to understand the chart shown here, I think because it has the dependent and independent axes inverted. To look at the number of peopl

It took me a few minutes to understand the chart shown here, I think because it has the dependent and independent axes inverted. To look at the number of people of a given age in a given year, you follow the line for that year, go down the left to find the given age, and see where it lines up at the top to get the number of people. The shading between the lines is irrelevant and just serves to confuse: the area under the line doesn't mean much.