A React component renders an SVG circle that tracks the mouse position across the full viewport. The circle’s center coordinates update via React state, with the `onMouseMove` event handler feeding client coordinates into a `useState` hook. D3 v5 provides the `arc` import, though the visible geometry relies on plain SVG circle elements. The example demonstrates bidirectional integration of D3’s ecosystem with React’s declarative state management, using the `useCallback` hook to optimize event handling. No data source is involved; the visualization is purely interactive, responding to user input in real time.