The economic relevance of the port sector is usually measured on an aggregated level by indicators such as added value, employment and investment. This paper tries to define the economic relevance for the regional as well as for the national economy on a disaggregated level. It attempts to identify, quantify and locate the mutual relationships between the various players in the port and between these players and other industries. Finally, it proposes a method to measure the effects of changes in port activity at a detailed level. A sectoral analysis is made by compiling a regional input-output table, using a bottom-up approach. The most important customers and suppliers of the port's key players or stakeholders are identified. A geographical analysis can be made by using data on a disaggregated level. Each customer or supplier can be located by means of his postcode. In this way, the economic impact of the port is quantified. In the case of the port of Antwerp, the results show important links between forwarders and agents. The geographical analysis shows agglomerating effects in Antwerp as a transhipment location point.