This visualization combines a line chart and a pie chart to show population changes over time by region. The line chart displays population trends from 1950 to 2100, with a vertical selector line that updates the pie chart to show the population distribution for the selected year. The pie chart uses `d3.pie()` and `d3.arc()` to render the regional proportions, while the line chart leverages `d3.line()`, `d3.curveBasis()`, and `d3.axisBottom()` for axes. Data comes from UN population estimates and medium-variant projections, processed via `d3.csv()` and `d3.timeParse()`.