This interactive line chart displays global population trends over time for different regions, with lines colored by region and a vertical black line marking the currently selected year. Users can move the mouse across the chart to change the selected year, which updates the line position and triggers a re-render. The visualization uses d3 v5, including `scaleTime`, `scaleLinear`, `axisBottom`, `axisLeft`, `line`, and `curveBasis` to draw the axes and paths, with `nest` and `schemeCategory10` for grouping and coloring regions. Data is loaded from UN population estimates CSV files, processed by melting year columns into rows, and rendered using SVG with a custom line chart component that handles the mouse interaction via `on('mousemove')`.