This visualization shows population over time by region, with multiple lines depicting trends from 1950 to 2100. The code uses D3 v5 APIs including `scaleTime`, `scaleLinear`, `line`, `curveBasis`, `nest`, and `axisLeft`/`axisBottom` to render SVG paths with a color legend. Data comes from UN population estimates and medium variant projections, processed by melting wide-format CSV data into tidy long-form rows.