# There’s just something about well drawn diagrams.

September 1, 2021

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Sam Frentzel-Beyme

# The Cognitive Science of Good Diagramming

## The Short of It

• Language explanations are more difficult to understand when dealing with placements in space.
• Diagrams allows for quicker understanding in terms of relationships between objects.
• Good diagrams work because they remove any extraneous details that get in the way of clear understanding.

There’s just something about well drawn diagrams. They convey information easily. They create a relatively level playing field in terms of overall systemic comprehension. And they are engaging enough that they allow multiple parties, even those with diverse interests, to begin conversing around a subject almost immediately.

But is there a science behind it?

It appears so. Jill Larkin and Herbert Simon wrote a paper in a 1987 issues of Cognitive Science called Why a Diagram is (Sometimes) Worth Ten Thousand Words in which they compare “sentential” representations, which means they basically wrote things in sentences, and “diagrammatic” representations, which, as you might have guess, used the typical diagrams we imagine.

He gives the following example written out in sentence form (see if you can construct it without cheating):

1. The first weight is suspended from the left end of a rope over Pulley A. The right end of this rope is attached to, and partially supports, the second weight.

2. Pulley A is suspended from the left end of a rope that runs over Pulley B, and under Pully C. Pulley B is suspended from the ceiling. The right end of the rope that runs under Pulley C is attached to the ceiling.

3. Pulley C is attached to the second weight, supporting it jointly with the right end of the first rope. Here’s what the looks like.

If you're eyes immediately started glazing over, here's what the translates to.

What's immediately evident is how much more difficult the language-based version is to get through, especially when dealing with placements in space. On top of that, what if you had to solve for something (Larkin and Simon suggest: Find the ration of the second to the first weight if the system is in equilibrium)? Now imagine trying to have a conversation with multiple parties about the content of those three simple sentences. What if it was a conference call?.

For most groups, a large part of the conversation would revolve around interpretations of language and connections between various structures. In other words, a lot of time would be spent on clarifying. Holding complex images clearly in working memory, let alone being able to manipulate them in real time, is something that takes a lot of work and practice.

Larkin and Simon’s take on what makes diagrams so great? They have three main reasons:

1. Diagrams can group together all the information that is used together, which means you can avoid a large amount of the searching for the elements needed to make the connections.

2. Diagrams typically use location to group information about a single element, which avoids the need to carefully match labels by area

3. Diagrams automatically support a large number of perceptual inferences, which make it easier for people.

In the end, Larkin and Simon believe that what makes good diagrams, and by the same measure good design, so powerful that they produce perceptual understanding without need for a lot of detailed direct explanation and this means you get something for nothing.

Looks like there's a free lunch after all.