has 2D boundary A 2D boundary may have holes and gaps, but it must be a single connected entity, not an aggregate of several disconnected parts. David Osumi-Sutherland Although the boundary is two-dimensional, it exists in three-dimensional space and thus has a 3D shape. a relation between a material entity and a 2D immaterial entity (the boundary), in which the boundary delimits the material entity my body has 2D boundary the surface of my skin mereotopologically related to