In the year 1900, just 13% of the global population lived in urban areas. This percentage has been constantly rising, and by 2005, 49% of the global population lived in cities. It is expected that in 2030, this number will increase up to 60%. Local governments and private companies invest large amounts of money to provide public services (like water, electricity and gas) to the citizens. These utilities are usually supplied via complex distribution networks that cover the entire cities. The water distribution system of New York, for example, is made up of an extensive grid of pipes stretching approximately 10500 km. The design and the expansion of these distribution networks represent a difficult challenge due to all the considerations that must be taken into account. The networks must provide a reliable service to (most of) the urban area, must comply with local regulations, should be easy to extend and are required to implement several safety measures. This should be done, naturally, at the lowest possible cost.
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