Wall Hangings
Besides the height of the wall hangings, there is also the pattern they are arranged in which, could bring into play a rectangle, diamond or even circular shape.
Room Layouts
Geometry in room layouts can be as simple as decorating in a square or in a circle, or more involved if there are hexagonal windows or a view that needs to be incorporated into the design of the room. Placing an entertainment stand at an angle in a corner is an example of using geometry. Angles must be measured, and space and distances need to be maintained. Room layouts also involve linear designs for separating areas of the room.
Symmetry
Choosing pieces of furniture and decor for a room involves geometry as you figure out the space and symmetry required to make each item part of a complete room. Height, width, flow, angles--all of these have to be taken into consideration to create an aesthetically pleasing room. Interior designers have to look at all of these areas and infuse geometrical thinking in their decor to make the designs complete.