This choropleth map colors world countries by income group using a spectral ordinal scale, with a hover effect that highlights individual country borders and a legend showing the color categories. The visualization uses d3.geoNaturalEarth1 and d3.geoPath to render TopoJSON world-atlas data, while d3.zoom enables panning and interactive exploration. Color encoding and the legend are built with d3.scaleOrdinal and d3.schemeSpectral, with data loaded via d3.tsv and d3.json.