I rarely make maps at the "entire world" scale. Most of my maps have been of a continent at the largest, and a castle at the smallest, with regions about the size of a country being about average. My average map is done at 1600 x 1400 pixels. Enough to blow up and show detail, but still be able to at least get an idea of most things when viewed in a smaller size.

If you are working on a continent scale or larger, you just won't be able to reliably have superb detail about everything. At least without an incredibly massive file size. You won't see individual trees at scale. You can see forests, and you can give them a somewhat abstracted texture that represents "there are a lot of trees here" but you won't get individuals. You won't want to try to label every town. Probably just capitols and important ports. Things like that.