Melting Data for Multiple Lines
This example shows population over time by region as multiple lines, with regions sorted by their final population and a color legend on the right. The visualization uses d3.line with curveBasis to generate smooth paths, d3.nest to group data by region, and d3.scaleOrdinal with schemeCategory10 for colors. Data is melted from wide UN population CSV files covering 1950–2100, combining estimates and medium-variant projections.