A 1963 drawing program changed every copy of a symbol the moment you edited one, and kept the wires attached when you moved it

Open the abstract of Ivan Sutherland’s 1963 thesis and one sentence does the work of an entire product category: “Any change in the definition of a symbol is at once seen wherever that symbol appears.” Sutherland wrote it about Sketchpad, which he built for his PhD at MIT. The thesis was completed in January 1963, according to IEEE Spectrum.

The setup sounds almost primitive. A user “sketches directly on a computer display with a ‘light pen,’” the abstract says, and “a set of push buttons controls the changes to be made such as ‘erase,’ or ‘move.’” Spectrum adds that Sketchpad ran on the TX-2 at MIT’s Lincoln Laboratory, and that Wesley Clark gave Sutherland access to the machine. The Computer History Museum describes the same thing: line drawings made in real time on a CRT, using a light pen for direct input on the display. Except for legends, the abstract notes, “no written language is used.” Nobody typed a command. You pointed.

The symbols are the part that still lands. You could define one from any collection of line segments, circle arcs and previously defined symbols, and use as many as you wanted. Edit the definition and every placed copy changed. That is find-and-replace with the replace already finished, no confirm dialog, and it worked on a machine whose display was a cathode ray tube you poked with a pen.

Then there is the topology. “Sketchpad stores explicit information about the topology of a drawing,” the abstract says. “If the user moves one vertex of a polygon, both adjacent sides will be moved.” Move a symbol and “all lines attached to that symbol will automatically move to stay attached to it.” Wires that stay wired are the whole reason a diagram tool beats a pile of loose lines (and the reason every unattached arrow in a slide deck makes people sigh).

Sutherland also let the drawing argue back. To make two lines parallel, the abstract says, the user “successively points to the lines with the light pen and presses a button.” The conditions stay displayed on the drawing, so they can be erased or changed later. Any combination of conditions can be defined as a composite and applied in one step, and because conditions can involve anything computable, he reported Sketchpad “has been used to find the distribution of forces in the members of truss bridges drawn with it.” A pen, a few buttons and a drawing that does structural math.

The abstract is also frank about what the program was good for: “the most usefulness as an aid to the understanding of processes, such as the notion of linkages, which can be described with pictures.” It lists electrical, mechanical, scientific, mathematical and animated drawings as things people had made with it. Spectrum notes the dissertation even covers animated cartoons, including a winking girl. Sutherland’s own summary of the ambition was that the system “makes it possible for a man and a computer to converse rapidly through the medium of line drawings,” per Spectrum, which also points to the 60th anniversary in 2023 and says Sketchpad’s source code is available from the Computer History Museum.

Where this goes is easy to guess from the mechanism. Drawing tools that store relationships, not only shapes, are the ones that can hand a drawing to something else to compute on, the way Sketchpad did with its bridge forces and the way its abstract suggests it could feed circuit simulators. The tools getting smarter about constraints and reusable parts are walking the path the thesis already laid out, and the ones that still treat a drawing as a flat picture are the ones that will keep asking you to fix every copy by hand.

The University of Cambridge’s Computer Laboratory republished the thesis as a 149-page technical report in September 2003, with a new preface by Alan Blackwell and Kerry Rodden. The report’s page puts the abstract where anyone can read it for free, and the abstract has one last line about the pictures in the thesis itself.

“The many drawings in this thesis were all made with Sketchpad.”