[Imp]

Just a note KEEP CONTOURS is only available when using MAP GEN in the Extended Map Editor.

On the same theme if you want to do a quick map by hand doing a couple of passes first with the FILL TOOL set to scatter can quickly make the map look quite nice. Experiment a bit with scatter percentage & press undo if need to.
Example
Initial fill another terrain colour, repeat for anything else you want over most of the map - fill area large
Follow up fills to place things like trees, rough, orchard, buildings etc - fill area as required.

When doing things like trees rather than trying to fill the whole area you want can set smaller & place several times instead. This lets you adjust the scatter each time if desired say from fairly dense to light.

Once at this stage you can see how things should sort of flow & finish by hand. far faster than doing from scratch & you only need a rough idea of what you want at the start what appears will motivate you.