A spatial relation specifies how some object is located in space in relation to some reference object. Since the reference object is usually much bigger than the object to locate, the latter is often represented by a point. The reference object is often represented by a bounding box (oblique or axis-parallel).

It might be the case that a spatial relation is not fully applicable. Thus, the degree of applicability is defined which specifies from 0 till 100% how strongly a spatial relation holds. Often researchers concentrate on defining the applicability function for various spatial relations.

Commonly used spatial relations are:

• directional relations
• distance relations

Directional relations

Directional relations can again be differentiated into external directional relations and internal directional relations. An internal directional relation specifies where an object is located inside the reference object while an external relations specifies where the object is located outside of the reference objects.

• Examples for internal directional relations: left; on the back; athwart
• Examples for external directional relations: on the right of; behind; in front of

Distance relations

Distance relations specify how far is the object away from the reference object.

• Examples are: at; nearby; in the vicinity; far away