Here’s a cool chart I found on Wikipedia that shows the age/sex demographics of the US population over time. In a sense, it’s a 3D chart – 2-spacial, 1-temporal dimension.

There’s a common trope about not having enough working-age population to support the retirement of the Baby Boom generation, because there was a huge bulge in births followed by a decline in births. But, as this chart shows, immigration has filled in those “low spots” over time, so thanks to our high immigration rate there are enough people to take care of all those old Boomers as they retire. (Even the ones who protest against immigrants.)

(chart from Mediawiki Commons, creative common license)