This example maps California zip code boundaries, coloring each region light blue with a red hover highlight. It visualizes stroke mortality data by zip code, though the chart itself displays the geographic shapes without encoding the count values in the fill. The map uses a Mercator projection with d3.geoPath and d3.geoMercator, rendering SVG paths from a GeoJSON file of California zip codes. The stroke data is loaded from a CSV, and the map supports pan-and-zoom interaction through d3.zoom.