The exact design of the galactic arms is pure art, really. Neither the authors nor NASA have any idea what the arms really look like, because seeing things like that from within one of the arms is too darn difficult. Only some rough ideas of how the arms might be configured on a scale of tens of thousands of lightyears have been revised, and the final truth waits for futuristic technologies and discoveries.
In contrast, the locations of the stars actually listed in the Maps and Charts come from parallax measurements that in the latter case are basically final for any stars that fit within those pages. There's some uncertainty regarding "medium-distant" stars at several thousand lightyears, such as Alpha Cygni, so even Charts is unlikely to be the final word on that. And stars beyond that range are generally beyond the reach of science, too: their parallax is so small as to be undiscernible by modern techniques, so all we can tell about them is their bearing from Earth. But generally, those semi-distant stars in the Milky Way aren't part of the night sky anyway, and don't have names we'd recognize in Trek dialogue.
The placement of fictional stars is arbitrary, of course. Or rather, some 90% of the fictional stars have been placed using the criteria that the travel times derived from episodes make the best possible sense (which isn't always very good sense, due to various internal conflicts). Only about 10% have been sprinkled in at random.
Timo Saloniemi
