This line chart displays population trends over time for global regions, with a draggable vertical line enabling year selection. The chart updates dynamically as users hover, highlighting the selected year across all series. Built with D3 v5, it uses `nest()` for data grouping, `scaleTime` and `scaleLinear` for axes, and `line()` with `curveBasis` for smooth paths. Data comes from UN population estimates (1950-2100), with a color legend and axis labels rendered as SVG elements.