Urban systems are the locus of consumption and engines of economic growth in a globalized world. Major cities offer then the most striking examples of the environmental and energy problems that accompany intense urbanization: as cities grow the flow of energy and materials increase and pose serious problems to global sustainability. It is therefore critical to understand the interactions between the socio-economic urban development and environmental pressures, and to develop models that may explain these interactions. Early efforts led to conceptual models of cities as urban ecosystems. Ecologists have described the city as a heterotrophic ecosystem highly dependent on large inputs of energy and materials and a vast capacity to absorb emissions and waste [1,3]. Wolman was the first to apply an urban metabolism approach to quantify the flows of energy and materials into and out of a hypothetical American city with a population of one million. Systems ecologists provided formal equations to describe the energy balance and the cycling of materials . Although these efforts have never been translated into operational simulation models, they have laid out the basis for urban-ecological research. A critical challenge in this context is how to balance service levels, asset management (at times with a growing maintenance backlog), and resource efficiency with respect to materials, energy and cost. In this paper the outline of a spatially resolved model of urban systems is described.