This interactive line chart displays population estimates and projections for world regions from 1950 to 2100. Users can hover over the chart to select a specific year, which draws a vertical black line and updates the selected year used for sorting the color-coded legend. The visualization uses d3.line with curveBasis for smoothed paths, d3.scaleTime and d3.scaleLinear for axes, and a d3.mouse event handler to trigger year selection. Data comes from UN population estimates loaded via d3.csv.