A world map choropleth visualizes population estimates by country, with countries colored on a blue sequential scale, while nations lacking data appear in gray. The example loads country boundaries from TopoJSON via the `topojson-client` library and renders them with `d3.geoPath` in an SVG, applying a Mercator projection. Interactive tooltips display each country’s population value on mouse hover. The color mapping is derived from a `d3.scaleQuantize` scheme, and the map includes a graticule overlay for reference.