http://www.slideshare.net/muyora/basic-theory-of-architecture

1.The articulation of the surface of the ground or floor plane is often used in architecture to define a zone of space within a larger spatial context.

2.Elevating a portion of the base plane will create a field of space and define the boundary of its field and interrupts the flow of space across its surface.and if the surface continues up across the elevated plane