A line chart displays population trends over time for global regions, with a vertical black line marking a selected year. Moving the mouse across the chart updates this selection, recomputing the line’s position. The visualization uses d3.nest to group data by region, d3.scaleTime and d3.scaleLinear for axes, and d3.line with curveBasis for smooth paths. Data comes from UN population estimates (1950–2014) and medium-variant projections (2015–2100), rendered as SVG with a color legend for region identification.