I would have thought the comment explained itself but apparently not. Geometry is the shape of the level ie. the postioning of solid objects. This clearly does not have to be purely decorative and can be combined with an effect on gameplay as well as eye candy. In the case of this map there is quite a lot of solid objects which are used to make the map look more interesting but few if any that affect the gameplay. I don't understand what you mean with your last sentence but decoration and geometry are not neccessarily the same thing; geometry can be decorative whilst affecting gameplay, decoration can only affect the look of the level. Hope that clears things up for you :).