This example overlays red SVG circles on an OpenStreetMap tile layer using D3.js and Leaflet.js. It loads geographic coordinates from circles.json and renders each point as a fixed-radius circle positioned via Leaflet’s `latLngToLayerPoint` projection, which updates on map view changes using the `viewreset` event. The visualization demonstrates how to combine D3’s data-binding and SVG manipulation with Leaflet’s interactive map APIs for custom geographic overlays.