To characterise economic activities in which metropolitan areas specialise, recourse is commonly taken to categories like producer or (knowledge-intensive) business services, derived from efforts to differentiate the notoriously heterogeneous service sector. An alternative approach to categorising economic activities is explored in this paper, building on the notion of transactional activities theoretically founded in 'new institutional economics'. To test this approach, which surpasses the manufacturing-services dichotomy, the 328 occupations of the German classification system are reclassified into three main groups (transaction, production/ transformation and R&D occupations) and sub-groups thereof. Comparing the occupational structure of Hamburg and Germany reveals that production/transformation activities still predominate nationwide, whereas Hamburg primarily specialises in transaction activities. Specialisation is particularly evident in certain transactional sub-groups, like advertising or agents/brokers/auctioneers. For other sub-groups, like publishing or wholesale, habitually undervalued in urban research, specialisation is also significant, while decisive R&D occupations are less important. In sum, a new and productive way to represent and analyse the complexities of the spatial division of labour opens up.