This visualization displays population trends over time for multiple regions, with each region represented by a colored line. A vertical black line marks a selected year, allowing users to compare population values across regions at that specific moment. The visualization uses d3.nest to group data by region, d3.scaleTime and d3.scaleLinear for axes, and d3.line with curveBasis for the paths. A mouse-interceptor rect captures pointer movement and updates the selected year via d3.mouse, triggering a re-render. The data comes from UN population estimates and medium-variant projections, loaded with d3.csv and processed through a melt function to format years.