This example demonstrates the simplest possible D3.js visualization: a single SVG circle centered on a blank canvas. The code imports the `select` function from D3 v6 via an ES module, selects the `<svg id="viz">` element, and appends a circle element with a radius of 200 pixels, rendered as SVG. It showcases the fundamental pattern of selecting, appending, and styling elements using D3’s declarative API. The accompanying README links to a video for beginners, emphasizing the learning-focused intent of the minimal code.