This research analyses the structure of material flows between urban centres. It is based on the results of a French survey that describes shipments sent by firms accross the country. Its aim is to shed light on the organization of urban systems. While most of works on urban systems are focused on the most visible and obviously dominant cities, little attention has been devoted to the basis of urban hierarchies. The purpose of this paper is to help fill this void, by integrating higher and lower levels of urban hierarchy. In order to do this, freight flows are analyzed to understand what they highlight on the economic interactions between the urban centres. This research shows that the pattern of freight flows between urban areas in France is hierarchical, but varies depending upon whether the flows are generated by wholesale trade activities or by manufacturing. The differences are explained by the specific organizational characteristics of each of these two activities. Wholesale trade broadly reflects the traditional spatial organization of service activities, with interlocking areas of influence. The spatial organization of manufacturing flows is more complex, which can be attributed to the regional specialization of activities. it should be highlighted that many of the outputs of manufacturing are inputs for wholesale trade. The majority of manufacturing flows involve parts and semi-finished goods that are not distributed to the market but to other manufacturing units, or to large purchasers who then coordinate the distribution of these goods. The exception could be certain fresh food products (i.e. Dairy), which, in their final form (ready for consumption), have a market-based distribution structure, similar to wholesale trade.