This interactive line chart displays population trends over time by region, with a movable vertical line and circular markers that highlight the selected year across all series. Users click or drag on the chart to change the selection, updating the visualization in real time. The visualization uses the D3 v5 modules `nest`, `scaleTime`, `scaleLinear`, and `scaleOrdinal` to structure and scale the data, while `axisBottom`, `axisLeft`, and `line` handle axes and path generation. Population data comes from UN estimates (1950–2014) and medium-variant projections (2015–2100), rendered as SVG with semi-transparent strokes.