This example displays a choropleth map of the United States, coloring each state according to a value from a local CSV file. The code loads GeoJSON geographic data and uses `d3.geoPath` for map rendering, while a linear color scale maps data values to a light-to-dark blue gradient. The map uses SVG paths with white strokes, and states without corresponding data appear gray. It demonstrates loading external data via `d3.csv` and `d3.json`.