Urban sustainability is often reduced to a specific set of issues packaged in the notion of 'green city' or 'eco-city'. The architectural policy of Oslo, for example, emphasizes sustainability, and 'greenness' as marketable qualities which are exploitable in the city's self-promotion. But eco-cities are also experiments with future relationships between society, technology and nature. For architecture and urban design, the challenge is to look beyond immediate environmental 'fixes', and engage the public through representation, iconography and aesthetics and promote variety and experimentation with possible future green cities. The Compact City is a long-term strategy for changing the form of the city. It is based on the observation of a correlation between the environmental impact of cities and urban form. A difficulty in the development of eco-cities is the complexity of interdependent issues that make up sustainable development, from energy production, food production, economic viability and collective cultural issues, as well as personal consumption habits.