defined as a group of interrelated industrial enterprises or a geographic entity, such as an industrial estate, a science park, a city, or a region. Geographical propinquity, although not required for achieving efficiency improvements at the larger economic scale, facilitates the process in many cases by reducing the need for transporting people and materials and encouraging like-mindedness among those whose initiative is required. Like-mindedness may arise most readily from social interaction stemming from living or working close to potential collaborators, though electronic communication is already reducing the need for physical proximity in many instances.

This spatial aspect of industrial ecology has implications for land-use policy and environmental regulations. There is probably a limit to the extent to which living functions can coexist alongside producing functions. Due regard for environmental improvement may reduce the direct environmental penalties of living close to industrial activity, but a preference for some degree of segregation will probably remain.⁴

Environmental regulations should not needlessly constrain the potential for achieving the necessary systemic interlinkages, as controls on the movement of waste do. Waste is the intermediate material of the industrial-ecological nexus. In the United Kingdom and other parts of Europe, problems have arisen because the waste outputs of one process that are a potential raw material for another process have been classified as waste requiring handling procedures and documentation that may make its subsequent use uneconomical.

Energy has a special place in industrial ecology for at least two reasons. First, it is an essential ingredient of almost all industrial and commercial processes and is used in large measure directly by consumers. Very few people do not benefit from processes that are pervaded by human-manufactured energy.

The boundaries of industrial ecology do not stop at the factory gate; linking industry and its products with other areas of human activity is a key consideration. Table 1 shows the energy and electricity consumption of different sectors in the United Kingdom and the importance of electricity compared with other final uses of energy sources. The picture is broadly similar in other European countries.

The second consideration is that the original extraction or harvesting of the energy source, to usable form conversion, supply to consumers, and end use usually all have significant environmental consequences. Table 2 shows contributions to national air emissions from energy use and electricity production in the United Kingdom. This pattern is not necessarily replicated in other European countries, mainly because the United Kingdom currently relies heavily on coal for electricity generation.