Fork of Selecting a Year on a Line Chart
This visualization shows regional population trends over time as multi-line chart, with a vertical line marking the currently selected year. Moving the mouse across the chart updates the selected year, and a legend identifies each region's color. The code uses D3 v5 APIs including `d3.nest`, `d3.scaleOrdinal` with `schemeCategory10`, and `d3.line` with `curveBasis`, while the interactive year selection relies on `d3.mouse` and `scaleTime.invert`. Data comes from UN population estimates and medium variant projections, rendered as SVG elements.