This line chart displays population trends over time for global regions, using United Nations population estimates from 1950 to 2100. A movable vertical line marks the currently selected year, and moving the mouse across the chart updates the selection to the nearest year, re-rendering the visualization. The chart uses d3.line with curveBasis for smooth paths, d3.scaleTime and d3.scaleLinear for axes, and d3.nest to group data by region. A separate color legend identifies each region, with SVG rendering and d3.mouse handling for interaction.