A line chart shows population over time by region, with a vertical marker indicating the currently selected year. A pie chart beside it displays the population distribution across regions for that same year. Hovering over the line chart updates the selected year and refreshes the pie chart. The visualization uses D3 v5 APIs including `d3.nest`, `d3.line`, `d3.scaleTime`, the `d3.pie` layout, and custom legend and chart modules, rendering in SVG. Data comes from UN population estimates and medium-variant projections.