This interactive line chart displays population trends for multiple countries over time, with a color-coded legend identifying each nation and a vertical line marking a user-selectable year. Built using D3 v5, it leverages `scaleTime`, `scaleLinear`, `axisBottom`, `axisLeft`, and `line` with `curveBasis` to render smoothed paths. Data is loaded from UN population CSV files, and hovering over the chart updates the selected year to show values at that point.