Is there a limit to array size?
When I try to store large map data in an array, it crashes the emulator when it is too big

It depends what type of array you're trying to initialize. If you're putting this as a global variable this can be the cause.

Also it doesn't recognize bool as a type

Booleans have been introduced in c99 with a simple enum but are highly unportable since in C, any value is true and 0 is false.
In C++ it has became a specific type with operators overloading enabling this behavior to be standard.
I suggest you not to use the BOOL macros of Ndless and use int, short or char as your boolean.

int map[252][40] causes it to crash, but that just may be from something in my code.

You can use bkpt() to put a breakpoint and see what line causes the crash (using the emulator and the 'c' command).

I guess I'll see if int map[10080] works.

What are accessor macros?

Tab being the array?

How would I go about reading/writing an array to a file?
For writing, I have
   FILE * f = fopen("/documents/miner/mapdata.tns", "w+");
   for(j = 0; j < sizeof(map); j++)
      fprintf(f, "%d", map[j]);
   fclose(f);
   refresh_osscr();
but it crashes.
I don't know what I'm doing

sizeof gives size in bytes, not number of elements. You should really do:

for(j = 0; j < sizeof(map)/sizeof(map[0]); j++)

Edit: Also, I think your fprintf should probably print some whitespace too so you can actually read the numbers back later instead of getting an incomprehensible giant string of digits.

My my, someone should update the first post for Ndless 3 at some point...