How was new maps made and what is used to generate new textures and all?
It's fairly easy, for a completely new terrain it asks for 4 graphic files. Dirt, Grass, Rock, Snow. You can either make your own, or find some online, plug them in, and the game does the rest.
Our graphics are 1024x1024 seamless png textures.
And what trees will be on map or will there be any , you do that?
What trees will be on the map is decided by the Starting Condition that you choose, not the Terrain type.