A simple interactive visualization demonstrates pointer tracking by rendering a single circle that follows the mouse cursor across the full browser window. The SVG canvas fills the viewport using `window.innerWidth` and `window.innerHeight`. D3's `selection.on('mousemove', ...)` event listener updates the circle's `cx` and `cy` attributes to the cursor's coordinates. The example uses D3 v7's `select` to append and style the SVG and circle elements, showcasing basic event handling and attribute manipulation.