Placeholder Values

Is there such a thing in GH where you can draw a line with temporary or placeholder values?
Let’s say you want to draw a line of a specific length, but don’t know the direction or starting points because those values are contingent of that line being a particular length.

A line with only a length but without known start point or direction would fill space in a uniform way, as it would exist everywhere at once. Even if it were possible to define a line this way (it isn’t) I’m not sure what you could do with a space-filling entity like this. Or did I misunderstand the problem entirely?

EDIT: reading the discussion ensuing the same question on, it seems I did misunderstand the question. Move along, nothing to see here.