This example presents an interactive choropleth map of the world, coloring countries according to their income group using an ordinal color scale. Users can click a legend item to filter the map, dimming all countries that do not match the selected income group, and click again to clear the filter. The visualization uses D3’s `geoNaturalEarth1` projection and `geoPath` for rendering map shapes, with zooming enabled via the `zoom` API. Data is loaded from the World Atlas TopoJSON and TSV files, processed using the `topojson` library, and rendered as SVG in a React-based workflow.