The base plane is a defined as a horizontal plan laying as a figure on a contrasting background. When one originally thinks of a “plane”, one may think of it to be a flat surface, this is not a requirement though. A plane can be any regular or organic shaped surface that creates a base.
A single vertical plane is defined as something that articulates the space on which it fronts. So, a single vertical plane can be anything that creates a front to a space, rather it be a vertical wall or a large tree.
One quality of architecture, and to me the most important, is light. Light can make such a huge impact in any type of design, especially interiors. There are many things to consider when looking at light, such as the quality, the color contrast and more.
When discussing openings in space-defining elements, one option up for discussion is within planes. Within planes can be defines as an opening that can be located wholly within a wall or ceiling plan and be surrounded on all sides by the surface of the plane. So, to break this down, within planes is pretty much any plane that is located within another plan, but not touching an edge.