The Task Team on Classifications (TT-Class), develops and maintains guidance for the Siting Classification and Measurement Quality Classification of Surface Observing Stations on Land. The team collects Member experiences, fosters studies on environmental exposure, provides implementation guidance, collaborates with other expert teams on metadata, training, uncertainties, urban aspects, and hydrometry, and ensures harmonized, global application of these classifications in support of WIGOS and the WMO Strategic Plan.