This visualization uses D3 v5 to display cumulative COVID-19 vaccination totals over time for multiple countries, with each country represented by a distinct colored line. The line chart employs a time-based x-axis and a linear y-axis scaled to billions of vaccinations. The code uses `d3.csv`, `scaleTime`, `scaleLinear`, `scaleOrdinal`, `nest`, and `line` with `curveBasis` to render the SVG paths, while a custom color legend function shows the country categories. Data comes from a GitHub-hosted CSV of vaccination records.