This interactive line chart shows population trends over time for world regions projected through 2100, using data from UN population estimates. Users navigate by mousemove events that call `setSelectedYear` to update a highlighted vertical line, while a color legend identifies each region. The visualization uses d3.v5 with `scaleTime`, `scaleLinear`, `scaleOrdinal`, `axisBottom`, `axisLeft`, `line` with `curveBasis`, `nest`, `mouse`, and SVG rendering. Colors come from `schemeCategory10`, and the chart adapts via a state-driven `render` function.