This interactive line chart visualizes population trends over time for global regions, with a mouse-driven vertical line denoting the currently selected year. Moving the cursor across the chart dynamically updates the blue selection line, highlighting population values at that moment. The visualization uses D3 v5 with SVG rendering, employing `d3.nest` to group data, `d3.scaleTime` and `d3.scaleLinear` for axes, and a custom `colorLegend` module for categorical color encoding. Data comes from UN population estimates and medium-variant projections, spanning 1950 to 2100.