Working in the map editor, especially on larger maps, I got to thinking that a "flood" button/tool is needed.
For most map editing a brush size of 1-10 is usually sufficient. However, when starting a new map you may sometimes want to start with a new terrain rather than the default. I appreciate that this can be amended in the terrain config files, but a button to allow "fill whole map" with desired terrain would be easier.
Following on, when your terrains are fully painted to your heart's content, it would be fantastic to be able to select "fish" or "ground water" and then be able to "flood" the whole map with this resource wherever those resources can appear, accounting for immovables etc.
I can't imagine a scenario where you would want to do this, but you may also want to flood with trees, stones or even critters. But it would be a fun map to play ... possibly.
Just an idea.