This interactive choropleth map displays global income groups using a natural Earth projection, with a linked color legend that filters highlighted countries on click and enables zooming via `d3.zoom`. It loads world topology from the World Atlas TopoJSON and tab-separated metadata, processing features through `d3.geoPath` and `d3.geoNaturalEarth1`. Colors are assigned with `d3.scaleOrdinal` and `d3.schemeSpectral`. The legend, built with custom SVG groups, toggles selection states and updates opacity, while the map’s sphere and country paths respond to hover and interactive filtering.