A circle follows the mouse cursor across an SVG canvas in this React-based visualization. The app tracks pointer coordinates using a React `onMouseMove` event handler and stores them in component state with the `useState` hook. Each mouse movement updates the circle’s `cx` and `cy` attributes, repositioning it instantly at the cursor’s location. The visualization uses React 16.9 and D3 v5 for rendering, with the SVG circle set to a fixed radius of 30 pixels. No data source is involved; the interaction is purely driven by user input.