Line chart with multiple lines
This line chart displays population trends over time for global regions, with each region represented by a colored line and a legend identifying them. The data spans from 1950 to 2100, combining UN population estimates and medium-variant projections processed through a custom melt function. The visualization uses d3.scaleTime, d3.scaleLinear, and d3.scaleOrdinal with schemeCategory10, while d3.line with curveBasis generates the smoothed paths. Axis labels, grid lines, and a title are rendered via d3.axisBottom, d3.axisLeft, and SVG text elements.