I figured out that my previous approach to make a nice simulation was taking too much time and getting me in a big risk of boring me out of this game 
So for now I'm making it simpler just to get things moving, and then I'll come back to it later to add more complexity and realism.
I expanded the cell types to 7, now including desert, marsh and swamp.
I've also redone the sprites for each cell type and converted the map to an isometric style, looking much better 
Tomorrow I'll begin the simulation itself, so the game will actually start to come to life
