I have in front of me a map of an area in the Angeles National Forest that says at the bottom, "map not to scale." What, if anything, does "not to scale" properly mean on a map or diagram, and if people use it in incorrect ways, do they mean anything specific by it? I.e., is there a common misconception as to what it means?
I can think of two possible meanings for this phrase:
The diagram does not show proper proportions. For example, we could have an anatomical diagram of a human body with the head the same size as the torso, or the famous New Yorker cover painting, "View of the World from 9th Avenue."
The diagram is not full size. It's scaled down.
Interpretation 2 is obviously pretty silly in most of the cases where I've seen the phrase used. For example, I don't need a special warning label to tell me that the piece of paper on which the map is printed is smaller than the Angeles National Forest's real size. My guess would be that the correct meaning of the phrase is #1, but many people ignorantly use it to mean #2 or use it without any clear idea of what they think they're saying. In the particular example of the map I have in front of me, comparison with other maps seems to rule out interpretation #1 -- there don't seem to be any features on the map that are drawn out of proportion to other feautures.