>You don't just look at it, often to define it you need to look at the space it makes between itself and other objects.<
Indeed. You may be interested in the Wikipedia* entry for the Ryoan-ji rock garden - top photo and the paragraph that reads -
In an article published by the science journal Nature, Gert J. Van Tonder and Michael J. Lyons analyze the rock garden from the standpoint of visual perception. They use the medial axis transformation, a model of shape processing, to show that the empty space of the garden is implicitly structured, and is aligned with the temple's architecture.