Melting data for multiple lines
This visualization shows population trends over time for the world’s regions, with each region drawn as a distinct colored line and accompanied by a color legend. The data is loaded from UN population estimates and medium variant projections, then reshaped from wide to long format using custom logic. D3 v5’s `nest`, `scaleTime`, `scaleLinear`, `scaleOrdinal`, `line`, and axis functions render the SVG line chart. Lines are ordered by their final population value, and gridlines are enhanced with tick marks.