This part of ISO 19111 specifies the conceptual schema for the description of spatial referencing using parametric values or functions. It applies the schema of ISO 19111 to combine a position referenced by coordinates with a parametric value to form a spatio-parametric coordinate reference system (CRS). The spatio-parametric CRS can optionally be extended to include time. The intended users of this part of ISO 19111 are producers and users of environmental information. Parameters which are attributes of spatial locations or features@ but which are not involved in their spatial referencing@ are not addressed by this part of ISO 19111.