In this study, we use PGIS to evaluate and map stakeholders' preferences for seven Marine and Coastal Ecosystem Services (MCES) in the Peniche-Nazaré region, located on the west coast of Portugal. We develop an alternative approach based on the Shannon index to identify conflict potential without questioning stakeholders directly about perceived conflicts. The Shannon index allows us to identify not only areas with highly valued ecosystem services and thus with current conflicting interests, but also areas providing several services that, although currently less valued, may hold existence, bequest, and option values that are important to consider in future decisions. Moreover, despite the increasing use of PGIS, there are still lacking benchmarks to assess PGIS positional accuracy. In this study, we also compare the spatial data collected from stakeholders on one of the services considered - Food provisioning, with spatial data on fishing areas collected from another survey of individual fishers to assess our PGIS positional accuracy. We surveyed 27 local stakeholders representing a wide range of interests. Our results show that stakeholders value more Food provisioning and Leisure and recreation and that the places perceived more relevant for Food provisioning by the interviewed stakeholders coincide with those places that are used by fishers, showing positional accuracy for this service. The Shannon index's application proved useful in indirectly identifying conflict potential that is of utmost importance for Marine Spatial Planning. By anticipating potential conflicts, policymakers may be willing to limit the use of maritime space for particular activities.