This bar chart visualizes the ten most populous countries using United Nations World Population Prospects 2019 data. The chart uses horizontal bars, with country names on the y-axis and a formatted population scale (in billions) on the x-axis. Built with React and D3 v5, the visualization separates axes and marks into reusable components—`AxisBottom`, `AxisLeft`, and `Marks`—which render SVG elements. The linear scale maps population values, while the band scale handles categorical country labels with built-in padding. Tooltips display the population value when hovering over each bar.