Two map examples show how D3.js renders geographic data with TopoJSON and custom projections. The world map uses `d3.geoNaturalEarth1` and a sequential blue color scale to encode population values from a CSV, overlaid with a graticule. The US map uses `d3.geoAlbersUsa` with state boundaries from `us-atlas@3`. Both use SVG paths via `d3.geoPath` and a fixed tooltip on hover.