T. R. Girill
Society for Technical Communication/Lawrence Livermore National Lab.
Technical Writing: Figure Captions as Skill Builders
Science and engineering articles almost always include figures
(drawings, photographs, diagrams). And when they do, those figures
always have captions (concise but revealing explanations of what
the figures show and why). Who writes whose captions? The same
scientists and engineers who performed the work and drafted the
article. So analyzing figure captions, improving weak ones, and
constructing missing ones are all authentic, focused ways for
your students to hone their nonfiction descriptive skills.
Sample Caption Construction
An excellent example of exposing good-description techniques by
comparing alternative figure captions arises from Figure 5 of a
recent article about mapping traffic patterns by plotting anonymous
cellphone usage data (Richard Becker and 9 others, "Human Mobility
Characterization from Cellular Network Data," Communications of the
Association for Computing Machinery, January, 2013, 56(1),74-82,
DOI: 10.1145/2398356.2398375). This is an interdisciplinary
article with broadly understandable, interesting content--hence,
it offers a genuine but easy chance for students to practice
drafting or improving captions for a technical figure. (For
convenience, Figure 5 is available online at https://docs.google.com
First candidate caption:
Professional papers never have figure captions this descriptively
empty, but students often stop here. This caption gives just a
milestone number. It locates the figure in a series but offers
no help interpreting it.
Second candidate caption:
Figure 5. Project results.
This announces what the figure represents. But it still fails to
reveal how the authors developed the figure or to explain the
Third candidate caption:
Figure 5. Results of our attempt to estimate traffic
volume using cellphone data.
This better caption reveals what the figure is about. But it still
fails to provide any clues for interpreting the figure's specific
graphical features. Why does it look as it does and what useful
information do those features reflect?
The same good-description checklist that scaffolds drafting effective
article text can help students here when improving such weak figure
captions (see http://www.ebstc.org/TechLit/analysisGd.html ):
Organization--How is this figure put together? Figure 5
here is a MAP (not a shattered-glass pattern, for example) of a
specific real place (Morristown, NJ, a New York City suburb).
Content--This particular map shows commute route trip
density. Nevertheless, no absolute data appear in Figure 5.
Also, the colors represent nothing. Here the line widths do all
the work: they reveal the relative (not absolute) traffic volume
on each of several routes into Morristown.
Signals--Here is where a good caption can really mitigate
reader confusion. When I first saw this figure I guessed that the
very visible digits were route numbers. Actually, they represent
trip counts normalized to 1000.
So here is a more complete and more useful caption for this figure,
just slightly expanded from the one published with it by the
Fourth candidate caption:
Figure 5. Relative traffic volume on 12 commute routes
to the center of Morristown, NJ, as assigned by our
cellphone algorithms. Line widths are proportional to
the estimated volumes. Counts shown at the beginning
of each route are normalized to 1000 moving cellphones.
Connection to Standards
Because the Common Core State Standards span so many grade levels,
finding authentic "small-scale" practice activities--realistic yet
not overwhelming in scope--can be daunting. Figure-caption
drafting and improvement meets that need nicely. The total text
volume is low. The figure itself scaffolds the writing.
Nevertheless, as seen above, every aspect of effective nonfiction
description gets exercised in building a good caption. Likewise,
comparing alternative captions for the same figure practices
required nonfiction text analysis. Finally, replacing milestone
captions with something else still concise but much more revealing
is an activity that every student can try out in their own
notebook--where they are the first to reap the explanatory benefits.