The subject of the city as a complex ‘system of systems’ is widely acknowledged and has been studied for decades. One of the earliest ideas on the complexity of the city was articulated in the early 1960’s by Jane Jacobs  and defines the challenges for urban science to this day . Cities are becoming increasingly complex, especially due to numerous challenges experienced at a global scale, such as the Covid pandemic and climate change.
The intention of the following piece is to both revisit concepts and offer ideas on how we apply different approaches to the city to enhance urban inclusivity, sustainability and resilience. It is worth noting that my intention is for the brevity of the contemplated subjects to offer opportunity for future expansion and not to create the impression of superficial consideration.
The Natural City
Nature-based solutions (NBS) are widely defined as actions or solutions that are inspired by nature to address societal challenges, such as climate change, food and water security or natural disasters [3,4]. The UN Environment Programme (UNEP) report on nature-based solutions highlights how these solutions can assist cities in dealing with fundamental environmental challenges . An interesting study by researchers at the Urban Systems Lab (The New School, New York) looked at combining blue, green and grey infrastructure for disaster risk reduction and climate change adaptation in the urban context . The International Institute for Environment and Development (iied) produced a very informative paper on examples of how nature-based solutions are applied globally .
Nature Positive is a concept that is increasingly considered and defined by the process of not only stopping, but also reversing nature loss by “increasing the health, abundance, diversity and resilience of species, populations and ecosystems”  to ensure a visible and measurable path of recovery. The Interdisciplinary Centre for Conservation Science (ICCS) at the University of Oxford  emphasizes that the need for quantitatively demonstrated overall net gain is much more important than merely the idea of reversing nature loss and moving towards recovery. The Cambridge Institute for Sustainability Leadership also developed a Nature-Positive Hub that is committed to the subject. A dynamic to consider, especially in the urban context, is the continuous (negative) impact human activities will have on nature and the appropriate compensation required.
The Biological City
Biomimicry is one of the most fascinating concepts for solving complex problems and simply refers to nature-inspired innovation. Janine Benyus from Biomimicry 3.8 recently stated that it is essential that we are reminded that a sustainable world already exists in nature. Hence, biomimicry is a process by which the natural world is ‘consulted for advice’ on design, engineering and social innovation in the built environment. Leonardo Da Vinci studied the behaviour of birds to design the first flying machines.
The following are some examples of biomimicry in urban development:
- Architects are inspired to develop more efficient buildings by the manner in which termites cool their mounds by drilling holes 
- The enhancement of road network planning can be inspired by studying physarum polycephalum (slime mould) creating optimized networks for transferring nutrients 
- Vegetation building façades not only combat carbon, but also attracts birds and insects 
How could we identify more examples from nature to develop more resilient urban environments, such as honeycomb-inspired earthquake-resistant buildings? How could we enhance our approach to circular economy by transforming the linear systems of energy still used in the built environment to follow the example of closed-loop systems that ecosystems use?
How could we harness the biological concept of homeostasis in the urban context? What potential does homeostatic processes offer for the self-regulation of urban systems and subsequent maintenance of stability? Researchers from the Architectural Association School of Architecture in London highlighted that biological principles of homeostasis have the potential to be applied to generative design processes, resulting in architectural morphologies that are better suited for the environmental context . Considering urban space, how could homeostatic principles be applied to enhance the study of morphology? A good example is a recent PhD research study at the Open University, developing a computational evolutionary model to generate urban morphologies with embedded homeostatic behaviour .
Following on from the above, urban metabolism considers the city as if it is a living biological system. It provides a framework by which the inflows, outflows and accumulation of resources in a city could be quantified . Although Karl Marx and Friederich Engels were the first individuals to refer to processes that are known today as urban metabolism, it was from a sociological perspective . Patrick Geddes was the first scientist to describe urban metabolism by depicting energy and material flow within the urban context [17,18]. An opportunity was identified where the integration of spatially explicit urban metabolism data in urban planning can enhance resource-efficient development and also the management of open space. Researchers formulated a strategy for investigating how the use of GIS data can improve the application of metabolic studies in urban planning and open space management. They performed a GIS-based urban metabolism assessment of Mexico City (at city scale) by including data on vulnerable communities, communal land and indigenous areas . The image below reflects the urban metabolism plan for Brussels, co-led by Brussels Environment, Impulse, Innoviris and Bruxelles Propreté.
Symbiosis refers to the living together of two dissimilar organisms in intimate association or cooperative relationship between two individuals or groups . Whether we call it that or not, it is a concept studied on a frequent basis in the urban context – the relationship between motor vehicles and pedestrians or cyclists, the dynamics between different cultural groups in a city etc. There is also the potential for cities to address environmental challenges through the application of urban metabolism – the transformation of linear relationships between consumption and waste to a looped system when outputs are returned as inputs, such as wastewater recycling . How could symbiosis also be applied to the relationship between urban inhabitants and nature, promoting regenerative development? I believe that a truly symbiotic city would not only enhance its natural aspects, but also a sustainable urban economy and quality of life. The fictional city of Birnin Zana in Wakanda (Black Panther) comes to mind. Various subjects provided for continuous (and sometimes heated) discussion, but for me personally the fusion of nature and technology was quite remarkable and I also appreciated the walkability of the city.
The Scientific City
The interdisciplinary field of urban science has grown in popularity in recent years and contributes theoretical and practical knowledge to understanding and solving urban problems. In the book Urban Informatics, Prof. Mike Batty states that urban science “deals with generic theories of how cities are structured and how they grow and evolve in time, how they change qualitatively with respect to growth, and how their populations organize themselves in space” . The problems that urban planning needs to address are often revealed by these features. Conventional scientific method laid the foundation for the development of the most efficient tools and techniques in urban informatics. Prof. Batty points out that urban science, like any other science, articulates the relationships that define city components by using quantitative methodologies, which are validated by observing actual cities.
In his recent book , Luis Bettencourt argues that until recently our understanding of urban processes was very limited and highlights the importance of a deeper and systematic scientific engagement with cities.
“The power of scientific knowledge is not in its ability to solve specific problems but rather in that it forces us to change our intuitive frameworks and adopt new perspectives from which new transformative solutions become not only possible but often relatively easy.”
Luis Bettencourt, Introduction to urban science: evidence and theory of cities as complex systems.
The Technological City
Key to the growth of Smart Cities is the continuous development of technologies such as the Internet of Things (IoT), Artificial Intelligence and Geospatial Technologies. However, it is essential that the enhanced systematic and economic functionality of the smart city also considers two interrelated subjects: livability and inclusivity.
McKinsey’s Global Institute assessed how smart-city applications could affect the following quality of life dimensions :
- Improvement of Public Safety: data-driven policing, while protecting civil liberties
- Faster and More Efficient Commuting: digital signage and mobile apps providing real-time information
- Better Public Health: digital applications to monitor, help prevent and treat chronic conditions
- More Sustainable Environment: water consumption tracking applications and building-automation systems
- Enhancement of social connectedness: digital channels and platforms to communicate with local official or agencies
Tremendous opportunity also exists in the application of geospatial technologies and analytics to gain insights relating to the five subjects above. Public safety can be enhanced through mapping crime hotspots and potential patterns, for example. Traffic simulation and congestion visualization would aid commuter decision-making. Apart from monitoring applications, air quality mapping will aid decision-making in terms of public health. Spatial visualization of sensor readings will provide insights into water and/or electricity consumption and related patterns. The mapping of Twitter feeds (for example) could highlight problems in certain regions. Furthermore, the application of urban simulation could study crowd movement in urban spaces and plan evacuation strategies or placement of policing. When it comes to urban innovation, how could more global platforms such as Tomorrow.City for example be generated to target specific challenges?
The degree to which a city is socio-economically inclusiveness is closely related of course to the general quality of life in that city. How could technology be harnessed to promote inclusivity and address the ‘digital divide’, experienced especially in developing countries? For example, how could digital wayfinding include additional information to the location of public transport nodes, such as affordable commercial entities or fruit market locations? In Kolkata, India, postal codes were provided to more than 120 000 slum residents by a startup, helping them to obtain bank accounts, voting registration and document to access government services . In London a joint venture between design studio Ustwo and the Royal London Society for Blind People is assisting the visually impaired navigate the city’s transportation network, using beacons to provide audio instructions via a smartphone application .
The Social City
One of the most important characteristics of a sustainable city is the degree of social value it offers its inhabitants. Beyond the important subjects of employment and housing, how could we instill a sense of belonging through place making and promote community development through social constructs? Urban playgrounds not only enrich the lives of children (physically, mentally and socially), but also promotes interaction between parents and in doing so build a sense of community. Arup and the LEGO Foundation developed the Urban Play Framework and Playful Cities Toolkit in partnership with the Real Play Coalition to provide a range of resources for understanding the complexities of play in the city and also to guide the design of play environments .
Finally, designing cities for mental wealth and wellbeing contributes immensely to the social value of urban space. Restorative Cities is a fascinating book on the subject  and offers a robust scientific basis for the multidisciplinary field of urban design and planning for mental health. Furthermore, it provides a framework for defining and integrating the components of a restorative city and offers related guidance.
“What is the city but the people?”
Although this discussion categorizes subjects and consider them separately, it is quite evident that they are all related to each other and should also be addressed in that manner. This is by no means a comprehensive study on the complexities of the city, but rather an overview of interesting concepts that are and can be applied in the urban context to enhance our understanding of its processes.
 Jacobs, J., 1961. The Death and Life of Great American Cities
 Bettencourt, L.M.A., 2021. Introduction to urban science: evidence and theory of cities as complex systems
 Cohen-Shacham, E., Walters, G., Janzen C, Maginnis, S. (2016) Nature-based solutions to address societal challenges. Gland, Switzerland
 European Environment Agency (2016) Building resilient cities key to tackling effects of climate change. Copenhagen, Denmark
 Depietri, Y. and McPhearson, T., 2017. Integrating the grey, green, and blue in cities: Nature-based solutions for climate change adaptation and risk reduction. In Nature-based solutions to climate change Adaptation in urban areas (pp. 91-109). Springer, Cham
 Showkatbakhsh, Milad (2021). Homeostatic Urban Morphologies: An Evolutionary Model to Generate Urban Morphologies With Embedded Homeostatic Behaviours. PhD thesis The Open University
 Derrible, S., Cheah, L., Arora, M., Yeow, L.W. (2021). Urban Metabolism. In: Shi, W., Goodchild, M.F., Batty, M., Kwan, MP., Zhang, A. (eds) Urban Informatics. The Urban Book Series. Springer, Singapore
 Pincetl S, Bunje P, Holmes T (2012) An expanded urban metabolism method: toward a systems approach for assessing urban energy processes and causes. Landscape Urban Plann 107(3):193–202
 Geddes P (1915) Cities in evolution: an introduction to the town planning movement and to the study of civics. Williams and Norgate, London, UK
 Fischer-Kowalski, M. (1998). Society’s metabolism the intellectual history of materials flow analysis, part I, I 860- I 970. Journal of Industrial Ecology, 2(1), 61-78
 Otero Peña, D., Perrotti, D. and Mohareb, E., 2022. Advancing urban metabolism studies through GIS data: Resource flows, open space networks, and vulnerable communities in Mexico City. Journal of Industrial Ecology
 Batty, M., 2021. Introduction to Urban Science. In Urban Informatics (pp. 11-14). Springer, Singapore
 Roe, J. and McCay, L., 2021. Restorative Cities: Urban design for mental health and wellbeing. Bloomsbury Publishing