Show me such a map.

(For Baldur's Gate 1, which didn't have a summon limit)
Find an indoor area, repeatedly use a wand of summoning until the entire area is full, then polymorph into a bigger form.

(For Baldur's Gate 2)
As above, but you need to have a Projected Image or Simulacrum use the wand of summoning to get around the summon limit. Also, summons that last longer (like Animate Dead) can be helpful here.

*Shakes head* I... am speechless.

You'll still transform...

But where will the game place you?

I've never actually attempted any of the stuff you said and I'm not a computer programologist, but I'm guessing one of three things would happen:

1. Your character's sprite would sort of become corporeal and overlap with the sprites surrounding him/her.
2. The AI would calculate which area on the map your character and fits best, and telelport you there - even if it's an absurd distance.
3. The game crashes
4. Any combination of the above.

That was actually four things which means I am now officially a liar.

In Spellhold.

Number 2 is more or less what happens if you do fit somewhere on the map; the game moves you to the closest place you fit, even if it's on the other side of a wall. My situation rules out number 2 by stipulating that there is no such place.

Number 1 is unlikely, given how the game doesn't do that in any other case.

Number 3, the crash, is the most likely, but the game could also freeze, softlock, eat up all RAM and then crash, or place you in a spot that doesn't exist. I can't see that happening for two reasons:

1. Spellhold isn't on the same map.

2. Spellhold is only in Baldur's Gate 2; what about the other Infinity Engine games (including the original Baldur's Gate)?

Asylum. I was being sarcastic.

LOL *pushes + button* Why not just try it yourself and find out?

Maybe he got the joke and was being sarcastic back. Or, maybe he doesn't understand any jokes.