G-code (Laser Engraving / CNC)

G-code is the control language of numerically controlled machines (ISO 6983, also known as RS-274): a sequence of commands saying "move there", "turn the tool on", "run at this feed rate". Laser engravers, milling machines and plotters speak it, and the GRBL and Marlin firmwares understand it directly.

A map in G-code is not an image but a set of toolpaths. Every OpenStreetMap line becomes a tool path, and the machine repeats it on wood, plywood, acrylic, leather or anodized aluminium. That is how people make city plan panels, gift maps and relief models.

The file is plain text you can open in a text editor. First comes a header with the job parameters, then the map layers one after another, each with its own comment so the operator can skip a pass or reorder it. The commands are standard: G90 for absolute coordinates, G21 for millimeters, G0 for a rapid move, G1 for a working move, M3 and M5 to turn the tool on and off.

The geometry is fitted into the work area with margins along the edges, 300x300 mm by default, and the scale is chosen automatically so that the map fits entirely and keeps its proportions. Power is set per layer: roads run at full, buildings weaker, green areas very weak — which gives different depths on the material.