A comprehensive systems approach is a prerequisite for the development of sustainability policy strategies. Quantitative models are frequently proposed as useful building blocks in this regard. We examine the value of such models in a case study on regional sustainability carried out in cooperation with the administration of the dutch province of limburg.c with the participation of an interdisciplinary group of civil servants, we developed an influence diagram representing the region and compared this to the coverage of quantitative models used in provincial strategic planning. The significant discrepancies between the two types of system representation lead to a more diligent interpretation of results, help to improve the models, and set challenges for future model use in regional sustainability planning. This article provides policy makers with practical advice on strategic planning and encourages scientists to improve the models by developing new techniques for the integration of quantitative and qualitative analyses.