 Analogously to the classification of manifolds, in high "co"dimension (meaning more than 2), embeddings are classified by surgery, while in low codimension or in relative dimension, they are rigid and geometric, and in the middle (codimension 2), one has a difficult exotic theory (knot theory).Particularly topologically interesting classes of maps include embeddings, immersions, and submersions.Geometrically interesting are isometries and isometric immersions.