ABSTRACT
Spatial planning requires the insights and contributions of all affected parties the 'actors' discussed in this chapter. Sustainability is considered to be an example of one of planning's most complex, underestimated and misunderstood notions. It is used in this chapter to provide a context for information that is or should be made available for decision-making purposes in the planning process. While sustainability is widely embraced as a new paradigm of urban planning, it is also increasingly accepted as a fuzzy notion. The functional criteria illustrated in this chapter can be used to design a set of sustainability indicators that meets both substantive and procedural demands, balancing validity with political purposes. As sustainability is a fuzzy notion, sustainability-related indicators should be the result of argumentation, the balancing of thoughts and views and the outcome of consensus.
