This visualization shows population trends over time for multiple world regions, with each region represented as a distinct colored line and a legend identifying the regions. A vertical black line marks the currently selected year, and users can move their mouse across the chart to dynamically change that year. The code uses d3.line, d3.scaleTime, d3.scaleLinear, and d3.scaleOrdinal to render SVG paths, along with d3.nest to group the data by region. Population data comes from UN estimates and medium-variant projections, covering 1950 to 2100.