I Made a Pen Plotter to Draw Maps of the Moon

Sebastian Lague details a homebuilt pen plotter aimed at drawing spiral cats and, more usefully, contour maps from planetary data. The project starts with the Moon, then expands into crater contours and full map plots, giving a practical look at how a simple machine can turn raw data into physical output.

The build sequence walks through the base, belt assembly, stepper inspection, motor driver setup, and a custom pen holder before the first successful line draw. From there, the focus shifts to the software side: random walks, spiral-cat experiments, marching-squares contour generation, and path optimization to reduce wasted motion and improve the final output.

That mix makes the project relevant beyond hobby hardware. Tooling-minded developers and technical artists will recognize the same concerns that show up in procedural generation, plotting, and offline rendering pipelines: data simplification, path ordering, and artifact cleanup such as pen smudges. The finished plots cover the Moon, Mars, and Earth, showing how a small custom rig can become a data-to-art pipeline with surprisingly broad applications.