This example displays a choropleth map of U.S. counties, colored by yearly data values from 2000 to 2021. A vertical slider with a play button animates through years, updating the fill colors with a sequential scale. The map is rendered as SVG paths using d3.geoPath with geoIdentity projection, based on TopoJSON data from the us-atlas library. Hovering reveals county names, state abbreviations, and the current value via SVG titles, while state borders are drawn as a mesh overlay.