Yeah, I'll probably only work again on such a big map if I have a powerful Mac - or photoshop works with nanotechnology. Rather, the former will be the case, I guess.

I split my map up in three files: landscape (2,68 gb), borders (2,06 gb) and the labeling (1,68 gb). Interestingly, with 2k textlayers the filesize doesn't increase really much (only a few mb). The most place took the background layer. The landscape file was only 6k x 6k px and was enlarged finally to double size. I did some softing / smoothing than to retouch the traces of pixelation.

To work on the labeling file does at least demand the most patience. More than I have.

Thank you.