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Two different approaches to a more efficient use of space in cities:
Increasing compactness and density

Traditionally the western part of Holland dealt with its limited resources of space by expanding horizontally, turning water into land. In this century most of the internal potential has been used until the point where reclaiming met its environmental limits. The open water remaining nowadays is needed for nature, recreation and agriculture. For these purposes some of the older reclamations have even been put under water again. The only `wet' solution left, the reclamation of parts of the North sea, is highly controversial and equally expensive. In this relation a growing interest can be observed in expansion in the third dimension: multiple land-use.

Two main approaches resulting in a more compact and densely built-up environment are of special importance for the application of multiple land-use.

The use of `space left over after planning'
Urban planning practices of the sixties and seventies resulted in vast amounts of internal unbuilt space, scattered all over the city, so-called: `space left over after planning'. Since the eighties most Dutch cities are addressing these resources in connection with the `compact city policy'. It won't be very long before the first cities will run out of the relatively easy part of this inner potential. By then, cities will be faced with the difficult task of activating the remaining leftover space struggling with the noise, emissions and external risks of various kinds of infrastructure, facilities and factories.

The use of urban transformation processes
During the economic life span of individual buildings or larger parts of town, the strategic value of the location may change drastically, by the continuing growth of the city, the adaptation of new infrastructure, changing economics. In these situations new uses and densities will become feasible options preferable to technical replacement.
In this way, the Randstad, like many other urban areas, has already witnessed the transformation of inner-city industrial areas, harbours, abattoirs, public utilities, hospitals over the past ten or twenty years.
Transformation processes like urban renewal, densification and the altering functional use will continue to be around for years to come. They play an important role in adapting the city to the changing demands of the society it accommodates.

In the case of space left over after planning, the emphasis will lie upon removing environmental nuisances, hampering the underlying urban potentials. In the case of transformation, more can be expected of switching extensive land-uses for intensive ones and replacing low-density buildings by moderate- or high-density buildings, while retaining spatial and living qualities. Combinations of the two are also possible.