Can anyone make some suggestions on making a poster-mosaic of hiking maps? I have several Trails Illustrated maps of the southern Appalachians that I'd like to mount together as a seamless map/poster on my wall. Thanks!

Make sure theyre all the same scale, plus you need two of each kind for front and back

I'm in the process of doing the same exact thing, although not for the southern Appalachians.

One tip: Trails Illustrated make great hiking maps; however, they are my least favorite for hanging on a wall or being able to look at from a distance. The reason being that the trails lines and border highlighting (National Forest, Wilderness, BLM, county, state lines, etc.) are often printed on the map in such bold ink, that it leaves the topographic details too faint or (quite often) obscured by them. Worst case scenario is you get a 1/4" thick brown ranger district border abutting a 1/4" thick green Wilderness border running along a ridgetop, obscuring tiny topography lines that are themselves printed in 2-pt red ink. You can still see everything as a quick reference when you're out on the trail, but if you wanted to use the map to do a more careful appraisal of the region, you're in for a hard time teasing the terrestrial map out from behind the huge, obscuring political map.

US Forest Service maps tend to use a very balanced line width for everything, which makes for a more manageable wall map, but not all their maps are waterproof, or are as cleanly printed as those Trails Illustrated maps. There are other publishers too, specific to location. You've just got to do some digging on Amazon.