World population is rapidly increasing, and 80% of the human population will live in urban areas by 2050. While urban areas already face a number of challenges, we must now find durable solution to accommodate for this projected influx of people. This provides the opportunity for cities to re-imagine urban development while improving many societal aspects of our way of living. Here, I focus on a concept called sustainable neighbourhoods. The basic functions of sustainable neighbourhoods "Cities cannot be considered sustainable if their component parts, such as neighbourhoods, do not meet sustainability criteria" (Choguill 2008) . A sustainable neighbourhood is made of several sub-units, each playing a specific function. Homes, businesses, services, flora, fauna, street networks,…While simple in theory, many examples demonstrate that very often, in practice, neighbourhoods have but one specific function, such as an housing area. Many current modern cities are built around a business center, and housing located in the city surroundings. This leads to huge need for transportation, which comes with commuting costs and the associated ecological and social issues. One possible reason for this is that urban planning is controlled by many actors, subject to political and economical actors with diverging interests, and that the rapid urbanization is arguably driven by marketing interests rather than citizen-focused interest. This strategy don't give the time to measure all the long-term consequences for the citizen life and urban landscape. Overall, it can be argued that this way of planning the urban landscape reduces the resilience of the city which in return will increase costs on the long-term. Ideally, sustainable neighbourhoods should reflect the unique needs of their inhabitants and accommodate residential, commercial, and recreational uses. Housing, access to education and services, and business must therefore be all embedded within a very local and compact scale to avoid the need for motorized personal transportation and increase the resilience. We can imagine that if sustainable neighbourhoods are well designed, each unit could acts as a “city center” where the community gather. Now, changing our lifestyle, especially the way we work (e.g., work at home) and share spaces (e.g. sharing business spaces for example) should greatly contribute to achieve more sustainable neighbourhoods. Our behavior and our society organization may be more than half of the problem. The urban design of sustainable neighbourhoods Compactness. Sustainable neighbourhoods must be as compact as possible to avoid urban sprawl, reduce infrastructure costs and maintenance, and resilience. Urban sprawl costs the United States alone nearly $400 billion annually. Compare Houston and Barcelona, for example. Both cities have populations of around 2 million people, but Barcelona fits into one-tenth of the area of Houston. As a result, the emissions from Houston are several times greater than those of Barcelona. Sprawl increases infrastructure costs by 10% to 40% (source 1) and intensifies a city’s carbon footprint, whereas population density lowers per capita emissions and reduces infrastructure costs. Connectivity. Urban design should not only ensure compactness but also the connectivity and collaborative aspects of neighbourhoods, again, for increased resilience. Whereas homes, businesses, and services are increasingly far apart in sprawling cities, sustainable neighbourhoods function like ecosystems. Each component of a sustainable neighbourhood – people, buildings, flora, fauna, street networks – operates within a whole. To perform this planning effort across several neighbourhoods, urban planning software, big data and IoT could provide a great contribution. For example, by simulating the commuting of people in a given urban environment, you can predict/improve how good the connectivity is across neighbourhoods. This aspect of using algorithms to do so will be discussed elsewhere (link to come). Connecting residents to the surroundings neighbourhoods via public transport, bikeways, and walkways could reduce private passenger vehicle travel by 20% (source 2). But we have also examples where the city design does not allow the use of private vehicles in the first place within the city or city center (for example: Masdar, Amsterdam). This has numerous benefits for citizens, protecting public health by improving air quality and encouraging people to walk or cycle, but also it is beneficial to reduce the surface dedicated to parking spaces, roads, etc., and the huge costs associated to that (traffic lights, maintenance,…). Resilience and life-span. My opinion is that the diversity and the dynamism of the basic components/functions of a given neighbourhood will determine its attractiveness and life-span. To reach this goal, the combination of each component/function must be carefully planned beforehand. Recently, IoT and big data have greatly contributed to increase our understanding of how city are used, for example, by highlighting the unused spaces and times where people commute the most. Now, we must take advantage of this knowledge to design neighbourhood with enhanced life-span. Another important aspect to improve the resilience of urban areas will be our ability to predict the “novel functions” of neighbourhoods. In the future, I envision that sustainable neighbourhoods will have the possibility to produce and distribute energy (through solar, winds, but also vibration of sidewalk) and grow food with local greenhouse/aquaponic systems. Innovation is going fast, and while technological development can solve many issue they can also be part of the problem. Connecting technologies such as IoT is a good example because while useful it remains often implemented in small fractions of the urban landscape, and as a result only a small percentage of the population can benefit from it. Another example is the use of renewable energies such as solar energy within the urban environment. The installation and maintenance of solar panels is not often easy, and not all cities or building rooftops are designed for such installation. Therefore, we must project ourselves in the future and design buildings that will be able to accommodate for these technologies. Sustainable neighbourhoods versus evolvable city Recently, importance has been given to the “evolvability” of smart & eco-cities. An evolvable city is a city that can adapt to novel needs, and functions. For example, while beautiful many historical cities of Europe face huge infrastructure problem to meet the novel needs of the population (metro, movie theater, business centers, housing...). So how do we adapt sustainable neighbourhoods with changing demand? How to maximize the re-use the infrastructure of sustainable neighbourhoods? Theses aspects remain open questions, but it is my opinion that if sustainable neighbourhoods succeed in fostering many functions then solutions will be more easily found to adapt/accommodate some part of the neighbourhood to implement a new activity. Conclusion Providing affordable and decent housing for all urban citizens is a priority, but it must be done in a way that the neighbourhoods become a place where people enjoy to live in community. Moreover, neighbourhoods must meet a number the requirements of compactness, connectivity, resilience and evolvability. Because of these many challenges, I doubt that the people working at the city planning offices of any city have the required expertise to tackle all these issues, therefore I hope some initiative such as the projects carried by NEDO, and hopefully Cell City in the future, will help providing new plans to achieve sustainable neighbourhoods. Thank you for reading! I would be happy to improve this article from your comments! Arno Germond, CellCityHub Founder (source 1) New Climate Economy (source 2) Carbon Lock-in Due to Urban Development, Stockholm Environmental Institute, 2015 (source 3) Choguill C. Developing sustainable neighbourhoods. Habitat International Volume 32, Issue 1, March 2008, Pages 41-48.