And especially this:
[quote:h1kzdb62] It's the way that isometry is handled in the Tiled map editor, so it's definitely a good approach if you want to use that tool.
So all you really need is to convert the tmx to iso xy's using the formula Katala quoted.
But you also have to keep in mind that isometric maps aren't all set up the same way.
The user has to decide where x, and y start, and offset from there.
For example: regular 2d 0x, and 0y, would be the upper left, but in an isometric map that would literally be somewhere over in left field, as in not even on the 2d map.