This choropleth map colors countries by income group using an ordinal color scale derived from d3.scaleOrdinal and the d3.schemeSpectral palette. It renders geographic boundaries with d3.geoPath and a Natural Earth projection, with hover highlighting via CSS. The visualization includes an interactive color legend built with custom SVG code, and supports zooming through d3.zoom. Data combines TopoJSON world geometry with TSV metadata from the world-atlas package, and country names and income values appear in tooltips via SVG title elements.