A line chart shows projected population growth from 1950 to 2100 for the world’s major regions, distinguishing between historical estimates and future UN projections. The code uses `d3.csv` to load two datasets, a custom `melt` function to reshape wide rows into tidy time-series records, and D3’s `nest` to group by region. It renders smoothed paths with `d3.line` and `curveBasis`, scaled by `scaleTime` and `scaleLinear`, with an SVG color legend appended via `colorLegend.js`. Data comes from UN population estimates and medium-variant projections.