Bottom line: Find a tileset you like, find a graphics set, and expand graphics set for your modded creatures.
So I'm not quite sure how tileset assignment is decided. I get the basics, the RAWs refer to a part of the tileset via a number, but apparently there are multiple tilesets? I've only ever seen the one (curses600x800 or whatever the dimensions are), and I'm not sure what tileset is being referred to when the RAWs call a tile, it all seems to be using the same tag?
Yes, there many tilesets you can choose to drop in ``data/art`` folder, but you can only choose one at a time. It is chosen in
``data/init/init.txt`` with the [FONT:my_tileset.png]
There are also FULLFONT, GRAPHICS_FONT, and GRAPHICS_FULLFONT which are explained on the wiki. Only one is used at a time.
Note that "tile set" and "graphics set" are two different things.
In one case I do understand tile assignments, and that seems to be creatures (where it's just assigning a letter). However this raises another question, which is how are tiles being used for more then one thing. Is there really no tile usage overlap in DF?
There is VERY MUCH usage overlap in DF. E.g. bridges and walls. That's what makes tilesets difficult to make well.
I don't really know how tiles are determined beyond the very basics it seems like, and I'd like to figure out more, as I'd like to make a tileset for my mod at some point, and I obviously need to know how all this hooks up to do that!
See wiki (as you have). Tinker. See wiki again. Rinse, repeat.
In short...
1. RAW tile assignments don't seem to make sense to me, outside of letter assignments. I'll grab a tile ID from the tilesets page on the wiki, and it'll reference an entirely different tile then I was aware of.
2. RAW tile assignments make sense when there's a letter assignment ([TILE:'A'] or whatever), but I don't know how those tiles are being used for multiple things.....
Be mindful of which one is decimal (base ten) versus hexadecimal (base sixteen). Example, hexadecimal 20 (usually written 0x20) is decimal 32, which is the space character.
A good breakdown is on the wikipedia page for
IBM ASCII Codepage 437.
This is important. These are the numbers you see in raws.
There are exactly 256 tiles you can use, 0 through 255, and that's it.
3. There seem to be multiple tilesets? I don't know if these are legitimately multiple tilesets or just a tileset being used in a different way depending on what you're looking at (the biggest example I can think of is the overworld map vs fort mode viewing).
Same tileset. Exact same graphics file. Symbols just have different meanings in different contexts.
E.g. decimal charater 227 (hex 0xE3) represents the goblin Dark Tower in world view, but represents a cabinet in dwarf mode or adventure mode.
The Omega character (decimal 234, hex 0xEA) represents a Mountain Home (i.e. CAVE_DETAILED) in world view, but a statue in dwarf or adventure mode.
This use of extended ASCII is one aspect of the game being
"Roguelike".
Aside from what you've asked, there are also
graphics sets, which let you specify specific images for specific creatures, professions, undead status, and other things.
These are independent from the tileset, and are probably what you'd really want to customize for any of your modded creatures.
Good luck!