This interactive visualization displays a single circle that follows the mouse cursor as it moves across an SVG canvas. The circle’s position is updated continuously based on the user’s pointer coordinates. Built with React 16.9 and D3 v7, the app uses React’s `useState` and `useCallback` hooks to manage mouse-position state, while event handling is implemented via the SVG `onMouseMove` attribute. The visualization renders declaratively—when the mouse moves, the `cx` and `cy` attributes of the circle are recomputed, causing React to update the SVG in real time.