This visualization shows population trends over time for multiple world regions, with each line color-coded and sorted by its final population value. The chart includes axes with gridlines, a legend generated by a custom `colorLegend` function, and smoothed lines using `curveBasis`. Data is processed by melting wide-format CSV rows from UN population estimates into tidy long-form data, then nested by region with `d3.nest`. The visualization uses `d3.scaleTime`, `d3.scaleLinear`, `d3.scaleOrdinal`, and `d3.line`, rendering to SVG with D3 v5.