This is the root document of the The Geographic COmmon (GCO) https://schemas.isotc211.org/19103/-/gco/1.2 namespace, a component of the XML Schema Implementation of Geographic Information Metadata (ISO19115-1). Original implementation documented in ISO/TS 19139:2007 is refactored in this implementation for ISO19115-3 to remove dependency of base data types on GML (the only gml element used was the enumeration of nilReasons). GCO includes all the definitions of https://schemas.isotc211.org/19103/-/gco/1.2 namespace. Elements that are extensions of GML elements are defined in the gmw namespace in ISO19115-3.