This example combines Leaflet with D3 to create an interactive map of India using OpenStreetMap tiles. Following the D3 geoPath projection, it renders state boundaries from a GeoJSON source, with states highlighted in red on mouseover while the map pans and zooms. When the primary data fails to load, the code falls back to displaying hand-drawn street segments in Mumbai, using the same Leaflet overlay and D3 geoTransform projection to keep vector paths synchronized with the tile layer during zoom events.