Multiple semi-transparent lines show population change over time for world regions, with a categorical color legend identifying each region. The visualization uses d3.line with curveBasis to smooth paths and d3.scaleOrdinal for coloring, while d3.axisLeft and d3.axisBottom render axes with gridlines. Data comes from UN population estimates (1950–2014) merged with medium-variant projections (2015–2100), processed via a custom melt function. The code relies on d3.scaleTime and d3.scaleLinear for scales in this SVG-based chart.