sdd:vector
sdd:vector is the literal datatype of a 2D vector — two numbers, written "x y"^^sdd:vector. It is the value type geometry uses everywhere in the drawing standard (spec §4.5): the object of sdd:at (position) and sdd:size (dimensions) on scopes, sdd:Node instances, and groups alike.
Because sdd:at is the one position predicate shared across scopes and nodes, a single sdd:vector reading applies uniformly wherever geometry is materialized, including edge waypoints.