If you gonna do this with a tilemap, the graphics for the tilemap will look close to this.
https://www.dropbox.com/s/2vvcx1a2wo0xx ... .capx?dl=0
I am sure that i can not make every combination with this, still. So to be complete it is a bad example.
But, you just have to break up things so they can be rearranged as seamless tiles to make any seamless form, in 2D !
In the end. I dont know what you plan to do. But, if it involves dynamic Z-orders, the tilemap is out of the question to use.
Better use instances of a sprite. That way you can control the Z-order anyway you want to.
An example:
https://drive.google.com/open?id=0B1SSu ... mtWVnc1cDg
Using R0J0hound 's behavior.
behavior-isometric_t153967
My project will use dynamic Z-order and now i realize that with tilemap it will be completely disaster. Thanks for pointing that out! <img src="{SMILIES_PATH}/icon_e_smile.gif" alt=":)" title="Smile" />