Probably this: http://img3.wikia.nocookie.net/__cb20130310211733/finalfantasy/images/8/89/Balamb_Garden_FFVIII_Artwork_3.jpg
This is problematic however. After Balamb become mobile you can still access training zone, quad and etc. However, the 3D model of worldmap Balamb is only the core thing with class rooms, without other places. Maybe someone understand this? Because I can't imagine how does Balamb really look.
When Balamb "Converts" into the ship the following things happen...
The ring increases in size and moves to the bottom
The spire angles out to be the "tail"
The "cupcake" extends higher and changes shape
The domes are retracted into the ship
This is why you don't go down halls anymore when Balamb is in Ship mode. The quad isn't an external dome, it's inside the Balamb building proper (On the left side).
However, it's not a 1:1 transformation. The transformation is a bit "fluid" and things change by disappearing/dissolving. It's why the transformation sequence is so obscured.
