Space in photographs
With music, the space between notes is just as important as the notes themselves. Similarly, with photographs the space between the subjects is important.
But I think 'space' in music is easier to define to a point. With music we often use the word 'space' rather than 'Silence'. Except with Music, space in the music isn't simply conveyed by having silence between notes. Space can be conveyed though tempo and intensity and density (or lack off) of the sound.
Similarly, with photographs space isn't necessarily 'empty areas' of the frame. Although this is can be true at times it is not the whole story. Space can also be conveyed through the use of a pause, something that makes you wait before moving on to another area of the frame. How many times have you felt yourself wait at one area of a picture before moving on?
In addition, 'space' can also be conveyed by areas of the picture that are texturally dense but have nothing of particular for the eye to settle upon. I call these spaces 'wallpaper'. Wallpaper can be texturally rich, may even contain patterns, but ultimately, the eye tends to float over it because there is no one singular point of focus.
If I am to interpret the image above, I would say that the bottom two thirds of the picture is wallpaper. It is texturally rich but I don't think there is one particular area of the frame that I focus upon or more specifically, feel is a compositional anchor point.
I would also say that the sky and water are wallpaper. They are silent areas where there is nothing going on. They are just used to create a pause between the foreground and the background hills.
Even with the background hills, the black tones and the curving shape of the hills take the eye for a few seconds before we are pulled towards the groove marks in the green moss. So even the hillside is a kind of space in the picture.
It seems a picture can contain many things and yet still have a lot of space. For me, the main object of focus in the picture is the vertical grooves in the green moss on the hill. Everything else is there to just give context and space and although some of this space is texturally rich, it is ultimately wallpaper. Our eye spends just a moment in it, and is still free to move towards the main point of focus of the picture.