[soltakss]

What, you've never been to Million Sparrow City?

Realism is relative. However realistic you want to be, there will always be a certain number of people who will say "That mountain would cause a rain shadow so you couldn't have a forest there" or whatever.

I wouldn't be too hung up on realism.

Draw a map, put interesting things there, have very simple climates for different areas and that's about all you really need.

Also, I wouldn't make the land masses too big. Genertela is smaller than the continental USA and has too many cultures to roleplay meaningfully in any one game. Look at the ancient cultures of Eurasia - there are too many to write up and use in a campaign. I'd keep things simple and focussed.