They're "lined up" because they're all at precise distances from Sol, a precision that is not actually warranted because the distance calculations have several light-years error in them.
For example, suppose a certain star cluster has a bunch of stars are registered in a star catalogue with a distance estimated at 2150 LY, plus or minus 10 LY. But that amount of error is not compatible witht he ED starmap, because ED needs to know exactly where each star is, so ED will put all those stars at precisely 2150.00 LY from Sol, lining them all up in a plane. Suppose this same cluster had some more stars, all at 2160 LY plus or minus 10 LY, and some more at 2170 LY, and so forth. The end-result is a bunch of "planes" of stars all lined up together, stacked at 10 LY intervals, much like this one which everyone travelling the Colonia Road can see, as it's not far from the Eagle nebula rest stop.
When they imported the star data, they probably should've ran the numbers through a last-decimal-place randomizer to avoid this. Still, it's not bad for a first attempt.