When you want to add axes to your chart, D3 provides dedicated axis generators that work seamlessly with your scales. The d3.axisBottom and d3.axisLeft methods create horizontal and vertical axes, respectively. You pass your scale to these axis generators, and then call them on a group element (g) in your SVG. The axis uses your scale to determine where to place ticks, labels, and lines, ensuring your data and visualization stay in sync.

You can customize axes in many ways: control the number of ticks with .ticks(), change tick formatting with .tickFormat(), and style text, lines, or the axis path using D3's selection and style methods. This means you can match the look and feel of your chart to your needs, from simple black lines to colorful, branded visuals. Axes are more than decoration—they make your charts readable and meaningful by showing the scale of your data.