This example displays COVID-19 case counts as scaled circles overlaid on a map of US counties. The visualization uses `d3.geoAlbersUsa()` for projection, `d3.geoPath` to render state boundaries from TopoJSON, and `d3.scaleSqrt` to map case counts to circle radii based on data from a CSV file. County centroids, computed with `geoPath.centroid`, position the circles, while a `d3.zoom` handler enables panning and zooming.