Animating Japan's Population Pyramid From 1950 to 2070 — Why You Need Cohort-Specific Mortality to Get the 1950 Triangle

"Have you ever seen Japan's ageing?" — I knew the data, but I'd never watched the shape of the country's population pyramid actually deform in front of me. So I built a 250-line page that does it: year slider plus auto-play, 1950 to 2070, with the first baby-boom cohort visibly rising from the bottom of the chart all the way to the top. 🌐 Demo : https://sen.ltd/portfolio/jp-population-pyramid/ 📦 GitHub : https://github.com/sen-ltd/jp-population-pyramid Hit the ▶ button and watch the chart morp