By "correctly" I actually meant being able to fully map the stages including all the portions that are off-screen. It's one of my pet peeve about isometric games; they often depict gorgeous worlds full of details and architecture but the game often prevents you from seeing a large part of it, most notably along the stage borders.
That reminds me... Does anyone knows how isometric games usually keep coordinates in memory? I mean, if I wanted to change the player's position, would a game use simple horizontal and vertical values, or would it use internal X and Y values corresponding to how those axes appear on screen, meaning diagonally? I'm thinking about future projects, maybe...