This visualization displays the number of COVID-19 cases per US county using a choropleth map colored with a threshold-based scale. It loads US county boundary data from the `us-atlas` package and New York Times case data from GitHub, merging them via topojson features. The map is rendered as SVG paths using `d3.geoPath` with an Albers projection, and supports zooming via `d3.zoom`. Counties change fill opacity on hover and show case counts in tooltips.