Landscape ecology challenges the urbanisation processes and the activities of the infrastructure sectors. Infrastructure networks have a strong impact on the development of cities and landscapes. This impact is often positive in an economic sense but can be negative in respect of natural or recreational functions of city and countryside. The challenge for spatial planning is to locate infrastructure lines in order to safeguard the conditions for the less dynamic functions in and around the urban regions. This paper analyses the impact of network patterns on urban development patterns and on green patterns, taking the history of the Randstad Holland as an example. In history the central peat area of this region was hardly accessible. This fact has led over the course of time to a unique spatial pattern: the major infrastructure lines and the major urban settlements are situated on the rim of a Green Heart. This creates a high-quality setting for the economy and the urbanisation of more than 6 million people as well as for natural and agricultural functions. Such a combination of urban elements and infrastructure around a green core can also be found on other scale levels and in other regions. Constraints on access often correlate with restricted urbanisation and with a sustainable position for the green elements. In those cases that such a restraint is chosen deliberately, often five phenomena are visible: (1) Polarity: a spatial polarity between less dynamic and more dynamic functions. (2) Decentrality: a side position of the main infrastructure and urban centres and a central position for the green functions. (3) Equality: equilibrium in extension of urban and rural elements. (4) Continuity: the green areas are part of larger scale networks. (5) Formality: planning policies couple the planning of infrastructure and dynamic urban activities to the development of the less dynamic, green functions. Together, these five elements create a special approach of spatial planning that can be applied on various scales. It is possible to use these elements as a concept, a design tool to create sustainable conditions for the 'green' functions in and around city regions. Based on some examples, suggestions are made for a strategy for urban-rural (re-)development aiming at high-quality urban life and for the natural environment, in and around urban regions. Sustainable spatial patterns demand a planning approach that combines the planning of infrastructure and urban activities with the planning of their green counterpoint. (C) 2000 Elsevier Science B.V. All rights reserved.
