The two levels you note - for me highlight two distinct steps in how I go about doing any project.
I have to learn things about the subject first - then formulate it into a structure...
So bottom up first (brainstorm/mind-map), then top-down.
Unless I knew enough about the subject - there is no way I could do the top-down method - as that feels like a way to "spin my wheels" a whole lot until I can get traction on the subject.