This map app displays world country boundaries using a Mercator projection. It loads geographic data from the World Atlas TopoJSON file via `d3.json`, converts it to GeoJSON with `topojson.feature`, and renders each country as an SVG path using `d3.geoPath` with `d3.geoMercator`. The fixed 900x400 SVG canvas shows the full projection without interactivity or styling beyond default black strokes on a transparent background.