Zones
Creation
First you'll need to select the "Zones Selection Mode" in the top right (stone pickaxe) when playing fortress mode. And then you are presented with two options above the first two hotbar slots.
Mining Zone
You can set a zone to be dug from the top layer to bedrock. All professions except miners will ignore the zone. Unfortunately, it seems like a large amount of miners isn't beneficial due to the lack of teamwork in the AI.
Farming Zone
Here you can set a zone to be ploughed, and sowed, but here you can only set the topmost layer of dirt to be used. If the area is large enough, farmers will automatically place water in it. And any block you can't create farmland from will be ignored. Including snow! Once again, every profession except farmer will ignore this zone.