This choropleth map visualizes world countries colored by income group using D3.js. The map uses a natural Earth projection via `d3.geoPath` and `geoNaturalEarth1`, with country boundaries loaded from TopoJSON world-atlas data and income classifications joined from a TSV file. A color legend built with `scaleOrdinal` and `schemeSpectral` displays the categorical color scale. Interactive zooming is implemented through `d3.zoom`, and hovering over a country highlights it in red while a tooltip reveals its name and income group.