HPGL — Hewlett-Packard Graphics Language

HPGL is a plotter control language invented by Hewlett-Packard and publicly documented in 1984. It is not an image but a list of commands the device carries out literally: lift the pen, lower it, move to a point. Over forty years the language has outlived pen plotters and is still understood by vinyl cutters, laser engravers and CNC machines.

A map is exported to HPGL when the result has to be a physical object: the outline of a district drawn with a real pen on paper, a city silhouette cut out of film, a street plan engraved into wood. The file is text — you can open it in an editor and read every command.

The stream contains the IN, SP, PU, PD and PA commands: initialization, pen selection, movement with the pen up and down. Each map layer gets its own pen numbered from one to eight, polygons are closed, and point features are drawn as crosses about five meters across at map scale. Coordinates are written in plotter units — forty units per millimeter.

The format's limitations are stated honestly: two-dimensional outlines only, with no fills, raster or labels — older devices simply have no text commands. The physical color of a line depends not on the file but on which pen or which blade sits in the matching holder.