An AI system may need to reason about the physical constraints of a problem, for example, postioning of components in a circuit-design expert system , or obstacle avoidance in robotics. Physical constraints of irreguar objects can be more complex than more abstract constraints such as an inequality. However, the 2D or 3D nature of physical world can also lead to heuristics, for example absolute distance between locations as a crude estimate of travel distance.
Used in Chap. 18: page 296