What that fancy title - which I just made up - means, is how a photo creates a sense of movement, a flow for the viewer, who notices the various elements in the frame. Perhaps the idea of movement is something that you hadn't thought of (after all, we are still talking about still photography, right?), but it's a very important part of photographic expression.
View this image for a few seconds. Then move your eyes away, and view it again:
What was the viewing movement of your eyes? Which element did you see first, and which did you see second? This can be different for different people. But generally speaking, most people notice the boat first, then very quickly glance at its reflection before jumping up to the big white cumulus cloud. Then they move downwards and to the right, passing from the lake and ending up to the vegetation on the bottom.
Something like this, that is:
The two aspects of this we need to analyze are:
- why this happens (so that we are aware of it during our own compositions)
- what does this flow mean for the composition
The answer to the first query is the most straight-forward one. It all goes back to what we were talking about last time, that is weighing factors between compositional elements.
In the example photo above, the boat is naturally the first thing to notice, because of its well-defined forms (and its "artificiality" in the surrounding environment), as much as its placement, in the center-left of the frame. That its reflection is the second thing to briefly notice is much a side-effect, as attention is quickly drawn upwards, to the highly saturated sky and the contrasty white cloud. The eye then moves downwards, and viewing the lake is more of an intermediate step in the eye's (or mind's, rather) way to the highly textured vegetation on the bottom of the frame.
As to the second issue...
This is more important (as it implies how this virtual flow affects the composition), and it is, alas, often more difficult to define. The reason is, of course, that it is subjective. Meaning is subjective. Nobody, not even the photographer him/herself can tell you "this is how you're supposed to view it", or "it means this". At best, the photographer can say "this is what it meant to me". But each viewer is free to reach their own conclusions.
For me, the photographer of the image above, the flow from the boat to the sky and back to the shore somewhat enhances the feeling of adventure, the feeling of movement and action lacking from the scene depicted. The flow of viewing underlines what the photo conveys (in my eyes, always): "I wanna jump into that boat, start it, and disappear in the warm summer breeze, far away into the distance. I'm stuck here on the shore."
What does the movement tell you?