This horizontal bar chart displays the populations of ten countries from the UN Population 2019 dataset. The bars are rendered as SVG rectangles, with population values mapped to bar length and country names on the y-axis. The code uses D3 v6 and React, employing `scaleBand` and `scaleLinear` for scales, and a custom `Marks` component to generate the rectangles. A mouseover tooltip reveals the exact population value, formatted using D3's `format` function with a `.2s` suffix.