This map visualization displays world countries and oceans using an equirectangular projection. It renders a geographic world map where each country is a filled path with a black stroke, and hovering highlights the country in cyan. The code loads country boundaries from a world-atlas TopoJSON file and converts them to GeoJSON features using the topojson library. SVG elements are generated with d3.geoPath and d3.geoEquirectangular, with styles applied via an external CSS stylesheet.