The image is only as useful as the argumentative connection the speaker makes explicit

DECORATIVE VS. FUNCTIONAL

The test is simple: if you removed the image, would the audience understand the presentation less well? If no, the image is decorative. A decorative image makes a slide look finished. A functional image serves the argument. The difference is not which image is chosen. It is whether the speaker explains what the image establishes.

FOUR TYPES OF FUNCTIONAL VISUALS

Charts and graphs. Communicate numerical relationships that prose cannot efficiently convey. The chart reveals the pattern. The speaker develops what it means.

Photographs. Provide direct visual evidence for claims about real conditions, events, or objects. Functional when the speaker explains what specific thing the image establishes.

Diagrams and flowcharts. Show relationships, processes, and structures that text must describe inefficiently. Value is the spatial relationship between elements.

Data tables. Display the precise numbers the argument depends on. More honest than a chart when the claim requires specific figures.

THREE COMMON STUDENT MISTAKES

Wrong chart type for the data. A pie chart implies parts of a whole. A line chart implies change over time. Using the wrong type communicates the wrong relationship between data points.

Unreadable chart labels. Default chart settings are built for a laptop screen. Projected charts need axis labels at minimum 18pt.

Stock photo with no connection to the argument. A generic cityscape on a slide about urban policy relates to the topic without providing evidence for the specific claim.

PRACTICAL STARTING POINTS
  • 1. Require a one-sentence visual explanation for every image. “This visual establishes [specific claim] because [specific evidence].” A student who cannot write that sentence does not have a functional visual.
  • 2. Show the decorative-vs.-functional distinction side by side. Same slide, same topic: stock photo vs. specific evidence image. Ask which one supports the argument.
  • 3. Teach chart selection as a standalone lesson. Bar: compare categories. Line: show change over time. Pie: parts of a real whole, five slices max.
  • 4. Require minimum 18pt labels on all charts for classroom presentation. Default settings are built for arm’s length. Projected charts need larger labels.

Sources: Mayer, Multimedia Learning (2001); Tufte, Visual Display of Quantitative Information (2001); Reynolds, Presentation Zen (2008)