The example displays two interactive SVG maps in a single page: a world map using the Natural Earth projection and a United Kingdom map using the Mercator projection. Both maps load TopoJSON data from external sources—world-atlas for countries and a UK counties dataset—then render geographic features with D3 v7's `d3.geoPath` and projections like `d3.geoNaturalEarth1` and `d3.geoMercator`. Graticules and country/region outlines are styled via CSS classes, with hoverable tooltips showing feature IDs or names.