All of my map stuff is "flat" because it's a top-down view map. Rivers will basically be somehow "drawn" or "doodled" onto the tiles, maybe.
My weather is pretty okay actually. I have limited it to around 200 "particles" and each "particle" is drawn with several streaks of rain/snow/etc and randomised speed. Each particle block is actually fairly large to give the impression of more individual particles, but in reality there is like 10 streaks of rain or about 8 snowflakes per image.
So as far as having a blank tile set goes, I want to be able to specify a series of things - like terrain type (grass,dirt,sand,etc) as well as have points of interest (like a town that generates random(x) number of buildings). Everything is tile based so things like towns would, I guess, be generated from some kind of central "Seed point" and just spawn buildings around/near it until the conditions are satisfied. I can probably figure it out, but any tips on how you did your islands would be appreciated. Did you start with aLL water and place the land over it... or the other way around?