A Framework for Measuring Urban Sprawl from Crowd-Sourced Data

The amount of people living in cities by 1800 was roughly around 3 percent of the world population. This number has increased dramatically during the last centuries, and currently it is estimated that one out of two people lives in cities. Furthermore, according to United Nations 60 percent of the world population will live in cities by 2030. This situation brings new challanges on how to conceive cities that host such amounts of population in a sustainable way while sacrificing as little as possible the inhabitants’ quality of life. This sustainability should address to several aspects that can be classified as economical, social and environmental. The cities are and will be centers of economical activity, and thus should provide facilities for business, innovation and culture. Such economical development should benefit all the levels of the social hierarchy, preventing inequalities and social segregation. The environmental part concerns the efficient utilization of the resources as well as the minimization of the impact on the ecosystems that sourround such cities. A convenient public transportation network, the preservation of green areas, the recycling of waste or the use of renewable energies are some examples of means to reduce the cities’ environmental impact. Unluckily by taking a look at the current megacities, it can be easily observed that very few of them meet the sustainability characteristics formerly reviewed. This can be partly explained by the urbanism pattern that derives from the processes of industrialization. When a city experiences such industrialization, with the related economic growth and the expansion of transportation networks, the middle class tends to migrate towards the outskirts of the city, potentially to live in terraced houses sorrounded by green areas. Such a pattern is commonly referred to as urban sprawl, and it was first observed in London and Paris during the 19th century. Cities like New York, Chicago went through this process during the early 20th century, and so did most central and northern- European cities around 1970-1990. Nowadays urban sprawl might even be more prevalent in developing countries, as it is the case with Mexico City, Beijing, Delhi, Johannesburg or Cairo.