It's World Population Day—a UN holiday, like International Day of Friendship and World Toilet Day, that pretty much all of us can get behind. To mark the occasion, Radio Free Europe/Radio Liberty has developed an infographic that dramatically captures the global geography of age these days, first in a map, then in a mesmerizing series of boxes, and then in a bar chart.

The visualizations below show the percentage of each country's population that is younger than 14. And they illustrate a phenomenon I wrote about in June: Youth populations, at least as a percentage of total population, are shriveling in the United States and many European and Asian nations, while ballooning in regions such as South Asia and Sub-Saharan Africa. Consider two extremes that appear in the graphics below: Fifty percent of Niger's population is under 14, while 13 percent of Japan's is.

There's good reason to feel ambivalent about these developments. Aging populations are usually a product of longer life expectancy and lower birth rates, which in turn result from improvements in health care and family planning. But in these countries, fewer working-age people can translate into slower economic growth and severe strain on social-welfare services (think Social Security in the U.S.).