This example displays a choropleth-style map of California zip codes, with each region colored light blue and highlighted red on hover. The visualization renders stroke mortality counts for 2016 by overlaying zip code boundaries from a GeoJSON file onto a Mercator projection. The code uses D3 v5’s `geoMercator`, `geoPath`, and `zoom` to create an interactive, pannable SVG map, while stroke data from a CSV file is joined to the geographic features via zip code identifiers.