Sparked by a post I made on another thread, I did a quick search for "Surveyor" (and other terms that might apply), but only saw the geological/mining kind, partially suggested as a solution to the same problem as the "(d)ig (v)ein" designation that I'm looking for. This isn't one of them (though could easily be involved in that environment, too).
A Road Surveyor job-type/task/noble might be a preequisite when DF development reaches the point where players are asked to actively participate in through-route building, in the spirit of the "spirit of the fortress" aim specification rather than micromanaging constructions by continual construction and task desgination.
The code's already there for route pathing/creation, albeit in the World Generation part, and a little guy tasked (with a yet-to-be-determined level of autonomy) to looking at the route between two points (edge to edge or edge to a designated waymark like your Depot or an arbitrary junction-point) and consider designating (in)appropriate boulders/trees for smoothing/felling and road surface assigning can be historically justified by the Roman-era endevours along these lines. Possibly even allowed to make occasional ad-hoc ramp-carving designations (or bring such spots to your attention, for your fine control). This could be a a designated position (related to architectect, though I'm thinking not quite the same as) or perhaps an immigrant noble who comes in as the 'outside world' starts demanding a suitable route into/through your territory.
At that latter level, he could just turn up and wander over the terrain (with or without his own armed escort, but I can imagine 'problems' for the player if he dies to fauna or other hostile entities) and bring up mandate-like demands that an area of ground be made passable, or even be a right pain and mark boulders for smoothing/etc by your lot, and request that a road of <insert available stone> blocks be laid. Or some sort of bridge be created at some point or other. But there's plenty of scope for adjustment. (One who was tuned up to be a real pain could turn up with a crew of artisans from the Mountainhome who make the road without your interference, but also without your consent or control, and no reference to your current or future plans for a particular area of terrain. I'd imagine such an entity would be quite unpopular for players, and the first against the wall when the revolution comes!)
But it also stretches just to an architect-level 'magenta-guy' entirely under your control, for whom you could lay 'patrol-route'-like waypoints, to your own liking, and he'd wander along and make appropriate notes, requests and/or auto-designations regarding how 'best' your crew could make an N-wide route along that line. Possibly related in precedence to an architect's tasks like an architect is to the eventual road builders when it comes to such constructions, or just aiding in prepping the ground and still needing the explicit architect/artisan road-making by the player.