Or, it contains "artist renditions" of data. Below is an example from Atkins' Physical Chemistry.
The best texts show actual data. Two of my favourite texts are: Biological Physics by Phil Nelson and An Introduction to Thermal Physics by Daniel Schroeder.
It is also interesting and disturbing that looking through the Australian edition of a popular introductory microeconomics text co-authored by Robert E. Frank [of Economic Naturalist fame] I could only find schematic graphs and no actual data.
Why does this matter?
After all, the figures look so much nicer and cleaner if they are just schematic. It is easier for students to understand them.
However, I think it is very important that students learn:
- Real science is messy.
- A theory is only as good as the experimental evidence for it.
- How to read, understand, and critique experimental data.