section_path: Infrastructure
section_name: Infrastructure
paragraph_text: Infrastructure
  
  Urban infrastructure involves various physical networks and spaces necessary for transportation, water use, energy, recreation, and public functions. Infrastructure carries a high initial cost in fixed capital but lower marginal costs and thus positive economies of scale. Because of the higher barriers to entry, these networks have been classified as natural monopolies, meaning that economic logic favors control of each network by a single organization, public or private.
  
  Infrastructure in general plays a vital role in a city's capacity for economic activity and expansion, underpinning the very survival of the city's inhabitants, as well as technological, commercial, industrial, and social activities. Structurally, many infrastructure systems take the form of networks with redundant links and multiple pathways, so that the system as a whole continue to operate even if parts of it fail. The particulars of a city's infrastructure systems have historical path dependence because new development must build from what exists already.
  
  Megaprojects such as the construction of airports, power plants, and railways require large upfront investments and thus tend to require funding from the national government or the private sector. Privatization may also extend to all levels of infrastructure construction and maintenance.
  
  Urban infrastructure ideally serves all residents equally but in practice may prove uneven—with, in some cities, clear first-class and second-class alternatives.