This line chart shows population growth over time for multiple regions, with a vertical line marking a selected year. Users can move the mouse across the chart to select a different year, which updates the line’s position. The visualization uses D3 v5 to render SVG elements, including axes, line paths with a curve basis, and a color legend. Population data is sourced from UN estimates and medium-variant projections, processed from CSV files. The chart includes interactive mouse events and uses D3’s `scaleTime` and `scaleLinear` for axes.