Representable relation algebras are characterised by a certain property of networks. Representations of relation algebras can be further classified as homogeneous or universal. These properties are also characterised by properties of networks properties (amalgamation and joint embedding properties). For the homogeneous, universal case a method of constructing interval algebras from point algebras is given. This is applied to give a metric algebra of intervals, a relation algebra capable of expressing Allen's interval relations as well as metric constraints.