Layers in “industry-standard” AutoCad and SketchUp are virtually identical (only that SketchUp cannot associate line types or widths with layers). AutoCad layers have no geometrical “separation” at all because AutoCad has no geometrical “interaction” either. In AutoCad you can draw a zillion lines that are on top of each other or cross each other and they stay separate whether they are on the same or different layers. And AutoCad is a fully 3D application and still calls its layers “layers”.
Anssi