It just needs to know how to orient each tile within the special, in case the mapgen was oriented differently or something.
Let’s step by step it.
You created a new location right? I’ll assume its more than 1 tile/location if you’re trying to make a map special. Okay. Those entries have an “id”, which we’ll need.
Now, you need to create an overmap terrain entry for each of those tiles. Here’s an example of one from my caches mod.
"name": "prepper cache",
The id has to match the id of the corresponding location entry (I always make them match, anyway). You have to do this for each tile you’ve created.
Then you create an overmap_specials entry where you tell the game how to stitch those locations into one large location as discussed above. Again, this “id” much match the id of the location, but also should have a direction tag after it.
You can see a full example of this on my github: https://github.com/TheMurderUnicorn/PrepperCache
I know there are examples in the core game, but my mod has these broken down into three files (which are smaller than the long lists in the game). C_caches has the locations. C_om_terrain has the om_terrain entries. C_om_specials has the entry where its all stitched together.
o_o That all sound very confusing? Probably. But hopefully that helps. . ?
Alternatively, you can show what you’ve been working on and maybe get some more targeted insight.