This example demonstrates how to build a scatterplot in React using D3 v4, displaying the relationship between city and highway fuel economy from a CSV file. The code creates linear scales for both axes, appends SVG circles with opacity and color encoding, and calls `d3.axisBottom` and `d3.axisLeft` to render the axes. The page also includes a basic SVG canvas with circles positioned via `selectAll`, `data`, and `join`, showing a simple data-binding pattern in plain HTML.