This choropleth map shows countries colored by income group, with a clickable color legend that highlights matching regions and a pan-and-zoom interface. It uses D3 v5 with `geoNaturalEarth1` and `geoPath` to project TopoJSON world data loaded from the World Atlas, while `scaleOrdinal` and `schemeSpectral` assign colors. A zoom behavior updates the map transform on interaction. The legend, rendered with SVG circles and text, triggers the selection filtering.