A choropleth map of U.S. counties shows COVID-19 progression stages across six dates in March–April 2020. Each county’s color encodes a stage from none to contained, emergence, outbreak, slowdown, or contraction, with a dropdown to switch dates. The visualization uses Mapbox GL JS for interactive vector-tile rendering and D3’s `d3.csv` and `d3-dsv` to load and filter county-stage data from a remote GeoJSON and CSV. Hovering highlights county outlines via Mapbox feature-state updates.