This example displays a choropleth map of California counties, colored with a sequential blue scale according to values mapped to each county’s FIPS code. The visualization uses data from the `us-atlas` package, loading county boundaries via `d3.json` and converting them with `topojson.feature`. The map is rendered using `d3.geoPath` with an Albers projection, and the color scale is defined with `d3.scaleSequential` and `d3.interpolateBlues`.