Hello. :B
You must have come here because you're interested in joining this mapping project, riiiight? Well... Why else? Anyway, My idea, Is that everyone who uses hammer, And POSSIBLY quark (Don't know if they can export to eachother), gets together and makes one big community map in segments. I'm already working on one segment, Which will be a replica of my house. :D
When you're done, Post the .map files here, And possibly a picture too. Segments can be any size, As I can always fill spaces inbetween them. Go as big, And as high as you like!
But most importantly, Have fun. :)