Shape

134 I What Makes It Visual?
forget what he’s done, so that he can see and do more—while the computer produced
drawing depends on the ‘‘topological and geometric structure built up in the computer
memory as a result of drawing operations.’’ This is precisely the difference between calculating
visually and calculating the way Evans does with predefined constituents. And
it’s what worried Wittgenstein—figures on paper don’t alter when you calculate, and if
they do, you remember what they were. It’s funny how things on paper—dirty marks,
shapes, and figures—bother Sutherland and Wittgenstein for the same reason: they
defy calculating. Of course, there may be an advantage. I can always count on the computer
drawing to behave properly according to the way it’s described. When its constituents
are fixed in drawing operations, its future possibilities are circumscribed once
and for all. The outcome of this is already clear in Evans’s shape
And whether or not I can calculate to reflect the shape
depends on how the triangle and chevron are drawn. Sutherland is correct. The difficulty
in making computer drawings is their structured nature. It’s hard—no, it’s impossible—to
tell what constituents to draw without foreknowledge. That’s the trick—not
to need foreknowledge, so that the properties of computer drawings can alter freely to
correspond with the properties of anything they’re used to describe. That’s why
embedding makes a difference in design. It guarantees that shapes do what you want.
There’s no structure to remember. There’s no reason for calculating to get in the way.
Figures on paper and the computer drawing are the same.
Herbert Simon likes the idea that shapes are represented (structured) and well
behaved in computers.
Since much of design, particularly architectural and engineering design, is concerned with objects
or arrangements in real Euclidean two-dimensional or three-dimensional space, the representation
of space and of things in space will necessarily be a central topic in a science of design. From our
previous discussion of visual perception, it should be clear that ‘‘space’’ inside the head of the
designer or the memory of a computer may have very different properties from a picture on paper
or a three-dimensional model.
The representational issues have already attracted the attention of those concerned with
computer-aided design—the cooperation of human and computer in the design process. As a