This choropleth maps cumulative COVID-19 cases by country, shading each nation with a red intensity proportional to its total case count. The visualization loads global case data from a cleaned CSV and aggregates it with `d3.rollup` and `d3.sum`, then renders geographic boundaries using `d3.geoMercator`, `d3.geoPath`, and a TopoJSON world topology. Hovering over a country reveals a tooltip displaying its name and total cases, while the SVG map updates fill colors via `d3.interpolateReds`.