The lines are distance markers, similar to stripes on a road, and serve a similar purpose. (Though, they don't divide lanes.)
I was watching them closely at one point on a planetary approach and noticed how they rolled in relation to your SC speed value. At the slowest point, in close to a planet where my top speed was restricted significantly, the line cycles seemed to be pretty close to 10 or 100 km intervals. I'm working off memory, so if anyone wants to poke at it, give it a shot. The slowest lines are pretty stationary at minimum SC of 30 km/sec. So the base value might be 1000 km/line.
The easiest way to verify this, would be to find a way to make the lines tick by at one line a second, and check your speed. Once you have that, it should be easy enough to extrapolate the scales on the lines as they shift up to higher and higher speeds.
I think it started at 1000 km between 'lines', then faded to 10000 km, then 100,000 and so on. Cycling up to light seconds and other such scale values.
As for the transitions of the lines in consideration to the fading, length, and slight positioning, I don't think that means anything. There's no meaningful way to isolate those metrics to indicate to the player anything useful. Rather, those features probably just exist to keep the lines from visually occupying the exact same spot when the scales are shifting up and down. Something to keep them from looking un-smooth and clunky. One of the big things I've noticed about the ED interface in terms of piloting. It tries very hard to keep motion fluid and organic. There is very little 'discrete' outside what is absolutely required. So it makes sense that the interface tries very hard not to give you any 'hard right angles' in terms of how things are presented.