This example visualizes global population trends from 1950 to 2100, showing how different regions change over time as multiple lines. The chart uses `d3.line` with `curveBasis` to draw smooth paths, with color encoding via `d3.scaleOrdinal` and a custom `colorLegend`. Data is melted from wide to long format using a custom `melt` function that processes UN population estimates from two CSV files, concatenating historical estimates with medium-variant projections. The visualization includes axis labels, gridlines, and a legend, with regions sorted by their final population value.