This visualization shows population change over time for different world regions, with multiple lines plotted on a shared time axis to compare regional trends. The chart uses a color-coded legend to distinguish each region. The code processes a UN dataset by "melting" the data from wide to long format, using `loadAndProcessData` to combine estimates and projections. It renders with D3 v5’s `scaleTime`, `scaleLinear`, `line`, and `curveBasis` for smooth lines, plus custom `colorLegend` and `axisBottom`/`axisLeft` helpers.