This D3.js v4 world map visualizes birth rates per country using a Mercator projection, coloring each nation on a white-to-blue linear scale. The map draws country boundaries as SVG paths from a TopoJSON-to-GeoJSON dataset, with the `d3.geoMercator` and `d3.geoPath` APIs converting geographic coordinates into planar shapes. Circular indicators mark four specific cities—Fairbanks, Boston, Philly, and COS—positioned via the same projection. The choropleth colors are derived from a CSV file loaded through `d3.json` and `d3.csv` deferred queues.