A choropleth map of U.S. counties shows COVID-19 progression stages—from contained to outbreak—across dates in late March and early April 2020. A dropdown menu lets viewers switch between daily snapshots, recoloring each county based on its stage. The visualization uses Mapbox GL JS for the interactive map, with county boundaries and stage data loaded as a GeoJSON source. D3’s `d3.csv` and `d3-dsv` parse the underlying dataset, while feature-state styling dynamically updates fill colors and hover effects on the vector tiles.