Decision makers in ports and airports are working in an extremely complex environment. Decisions involve multiple actors, who all have a different view on the system under investigation, and on the effectiveness and desirability of possible outcomes of the decision making process. Simulation and visualization are two core technologies to support these complex decision making processes. One of the major challenges is to provide the variety of involved actors with visualizations that fit their view on the system. Two case studies show that the visualizations should be able to provide two views on decision making: a view on the system under investigation and a view on the multi-actor decision making process itself. This paper presents the requirements for a service-oriented and Web-based simulation and visualization portal, which integrates both views. In cooperation with the Port of Rotterdam we are currently developing and testing a prototype implementation of the portal.