True. I was thinking of OP's apparent purpose, but it's worth knowing in case things change.
Two additional notes:
- Do not blindly ramp-out the initial layer-below-the-surface if it has trees (or 'boulders ? - not sure, but I've definitely maybe had problems with them) as undermining these causes cave-ins. I always channel the first level of surface away, and only then ramp-designate the layer below the newly revealed and fresh surface, free of such dangers.
- At each layer, whether channelled or ramped into existence, a 'full' tile will convert to a ramp, and any ramps now solely acting as ramp against the cell you just removed will vanish without your effort. But if you've got down to an isolated pillar (one-tile high, any more is an error leading to a cave-in) surrounded by ramps then that becomes a stand-alone ramp amongst flat ground. You'd have to remove it if you don't want it and aren't going to ramp out beneath it.
I commonly dig out 'sunken fields' in soil for aboveground farming purposes. Sat on the original surface there's often a boulder or other non-soil tile that you don't want, but if the soil exists as the filling of cells in the layer below (check!) then this will give a uniform ground across which a agricultural plots can be placed without such interruptions.
For a 5x5 plot, say, I clear trees
first (prioritising these over other trees, if necessary) then set up priorities of channelling in various ways, including:
####### #######
#55555# #15551#
#53335# #51315#
#53135# or #53135#
#53335# #51315#
#55555# #15551#
####### #######
These would each ensure that the only ramps needing removing are the ones beneath the 5s (next to the undisturbed #s) in the first pattern. The second pattern I often use to get the X-pattern (however large) to properly demarcate the digging area below for easier coordination. The 3, 5(, 7) prioritisation ensures a good order of 'retreat' towards the edge.
And, if I've dug out the 5x5 underside (I often dig several such - still
after the trees are cut, so there's no root systems and associated problems - to provide for underground farms which I can convert just the once into sunken 'overground' ones) that pattern of channelling also is proof against creating cave-ins of the surface tiles into the (rampless!) lower void.
But still take care the first time you try this sort of thing. You can easily make mistakes, as I have in the past.