environment concept for isometric game Thread

Hi,
I would like to learn how to create an isometric environment / map for a game. I understand the isometric concept, however I have issue when I have to draw the terrain (grass, river, etc...) or map borders (rocks, beach, etc...).
I would like to know if someone could help me with this topic, telling me the process or forwarding me to a forum or course where I could learn it.
thank you