This choropleth map visualizes changes in forest coverage between 2000 and 2010, with a dropdown menu letting users filter by varying tree-canopy density thresholds (from 0% to 75%). Each country is colored along a red-yellow-green diverging scale (via `interpolateRdYlGn`) to indicate whether that nation gained or lost forested area at the selected threshold. The map is rendered using `d3.geoPath` and `d3.geoNaturalEarth1` projections, with country shapes loaded from a TopoJSON world atlas and forest-loss data fetched from a CSV file.