This choropleth map shows world countries colored by income group, with interactive filtering controlled by a clickable legend. Selecting a legend category highlights matching countries while dimming others, and clicking again clears the filter. The map uses a natural Earth projection with an SVG rendering, drawing country paths via `d3.geoPath`. The color legend, built with `d3.scaleOrdinal` and a spectral scheme, triggers the filtering through an `onClick` handler. Country data comes from the world-atlas TopoJSON and TSV files.