Compact City as a Model Achieving Sustainable Development
There is not a common definition of compact city in literature, indeed this concept is one of the most discussed in contemporary urban policy. Nevertheless, the compact city model is expected to improve cities’ environmental, social, and economic performance, by influencing the use of space and by integrating different urban policies.
The compact city definition can be structured with reference to the following approaches: “to increase built area and residential population densities; to intensify urban economic, social and cultural activities and to manipulate urban size, form and structure and settlement systems in pursuit of the environmental, social and global sustainability benefits derived from the concentration of urban functions” (Burgess 2000, pp. 9–10).
The 2012 OECD Report on Compact City Policies gives a synthetic definition of the compact city as a “Spatial urban form characterized by ‘compactness’” and with some “key characteristics as: (i) dense and proximate development patterns; (ii) urban areas linked by public transport systems; and (iii) accessibility to local services and jobs” (OECD 2012, p. 26).
Therefore, the compact city concept in the framework of sustainable development does not only mean to enhance urban density but rather to combine the quantitative concept of density within other goals and requirements aiming to undertake high levels of economic viability, environmental quality, social equity in the urban environment.
The Controversial Paradigm of the Compact City
The compact city model has always been a controversial and discussed concept, characterizing the last 150 years of urban policies. More recently it has been associated with the sustainability imperatives thus gaining a wide consensus among the urban planning strategies developed worldwide and fighting against dispersed settlements and mono-functional suburbs. At the same time, also with the appearance of new urban issues, such as climate change effects and new territorial risks, it has received several critiques as well, making the compact city model more and more complex and rather discussed for promoting a real sustainable development.
From the Ancient to the Spread City
The compact city concept arose with the origin of cities. They were exemplified by dense and very small areas surrounded by walls, where residents carefully allocated space to residential areas, public squares, and roads. The main and widely recognized model of compact city is the medieval city. Indeed, in the Middle Age urban density within the city walls was high and the city was compact and mixed use since people lived and worked in a confined space. This dense structure encouraged concentration of activities and of new inhabitants rather than new expansions. This form was developed in most European cities during the seventeenth and eighteenth centuries, as well as the central parts of many older cities in North America, Australia, and New Zealand, to ensure destinations were within a reasonable walking distance (Newman 1992).
During the industrial revolution in the eighteenth and nineteenth centuries, city walls were gradually destroyed in all those cities where industrial, transport, and port activities were more developed. The original urban order and the ancient compact city form came to an end. These new economies attracted large numbers of people from rural areas, giving birth to a new and rapid urban growth, thus producing a physical explosion of the urban fabric as well as big health problems due to the lack of capacity in sewage and garbage disposal and the co-existence of polluting firms and overcrowded housing.
The spread development of passenger trains and trams coincided with massive urbanization throughout Europe, North America, and Australasia (Newman 1992).
During the nineteenth and twentieth centuries, the compact city became both a tool for containing uncontrolled urban expansions and a critical model to be overcome in order to ensure better urban living conditions. Consequently, greenbelt policies were developed in several European cities as a planning tool for limiting urban expansions through new green boundaries, following the removal of city walls (Kühn 2003). Ebenezer Howard theorized the “Garden City” concept, based on a greenbelt hosting agricultural and recreational activities developed around a city for limiting its expansion. The fundamental aim of greenbelt policy was to prevent urban sprawl by keeping land permanently open. Especially in UK, greenbelts have become an important part of the National policy during the twentieth century, but other European cities such as Vienna, Barcelona, Budapest, and Berlin have followed this tradition (Kühn 2003) and several other non-European cities such as Washington, DC, Tokyo, Hong Kong, Seoul, Sydney, and Melbourne adopted this policy (Tang et al. 2007). At the same time the Garden city theory looked beyond the city borders by foreseeing to establish new self-sufficient Garden Cities, which would house a socially mixed population and would be surrounded by greenbelts. This regional, decentralizing vision gained relevance not only in Europe but also in Russia, where the abolition of old cities and the dispersion of populations into the countryside was encouraged (Hirt 2007) and in the USA, where Frank Lloyd Wright theorized Broadacre City, a radical dispersal scheme where each lot was at least 1 acre. The influence of these utopias favored the uncontrolled spread of low-density suburbs, especially around North American, Australian, and New Zealand cities. Moreover, the introduction of the automobile occurred during the first decades of the twentieth century, ensured people to be not obliged to live in the city or close to a transit station anymore, but to escape pollution and noise by living outside the city, using their private motorized vehicle to reach their place of employment every day and any other destination. The direct consequence was the development of low-density suburban sprawl and the decentralization of cities since the early twentieth century, which characterized mostly North American, Australian, and New Zealand cities (Arbury 2006) as well as the European cities after the Second World War.
Rediscovering the Compact City for Achieving Sustainable Development
During the 1960s the negative effects due to urban sprawl became evident as a social issue, especially in the USA. Indeed, the sprawl of suburbs generated segregation, the loss of community values, and less leisure time, due to the longer commuting times. The planning theories and practices that strongly opposed to density in the urban context till the beginning of 1900 were progressively questioned and density has been rediscovered as a condition favoring the mix of human preferences, social diversity, uses, activities, etc. (Moroni 2016). The first endorsements to more compact settlements came from the social sciences. Indeed, Jane Jacobs, an American sociologist, argued that the city, with its vitality, mix of uses and traditions, rather than low-density suburbs, represented the most desirable form of development (Jacobs 1961), by implicitly referring to compact city’s main features. In her studies she supported compact city neighborhoods where different kinds of households and individuals live together, establishing relationships more easily than in dispersed single-use, single family suburbs.
Since 1970s, the awareness of the negative effects due to urban sprawl further increased, affecting not only social aspects but also environmental consequences, thus pushing towards the promotion of more compact settlements.
The 1987 World Commission on Environment and Development’s Our Common Future (WCED 1987), also known as the “Brundtland Report,” introduced the concept of sustainability to the broad public. Sustainability has been embedded in urban planning theory and the compact city began to emerge as the most sustainable model of urban growth, ensuring the two sustainability imperatives of resource conservation and waste-minimization (Burgess 2000). The compact city concept was widely discussed during the 1990s in many countries worldwide as a way to address urban sustainability (OECD 2012). In this process the European Commission played a key role with the publication of the “Green Paper on the Urban Environment” (CEC 1990) where urban containment policies and more compact forms are encouraged assuming that they make urban areas more environmentally sustainable and improve quality of life (Jenks and Jones 2010; Jabareen 2006). Indeed, as summarized by Jenks and Jones (2010, p. 2) “compact urban forms would reduce urban sprawl, protect agricultural and amenity land, and lead to more efficient use of existing, previously developed urban land. With a mixture of uses in much closer proximity, alternative modes of travel would be encouraged, such as walking and cycling, and public transport use would also increase. This in turn would lead to environmental, social and economic benefits.” This position has been assumed by urban planners and scholars all over the world who recognized a lot of advantages in intensifying the density of urban settlements. The most cited benefit was that the compact city model is more sustainable in terms of energy consumption and pollution than suburbs (Breheny 1995; Newman and Kenworthy 1989). Indeed, denser cities could optimize energy and transport flows by taking advantage from the reduced distances among dwellings, work places, businesses, and public services and facilities, thus enhancing public transport, and consequently by reducing air and noise pollution and increasing protection of agricultural land and open spaces (Burton et al. 2000; Jenks and Burgess 2000; Neuman 2005; Churchman 1999; Breheny 1992; Conticelli et al. 2017).
Consequently, another important aspect characterizing the compact city model is the mix of different urban uses. Generally mixed-use development is able to reduce travel times and to support more sustainable means of transport by locating businesses services and workplaces among residential areas, overcoming the rationalist separation of the urban functions or the single-use suburban city model.
Denser mixed-use environments achieve also social and economic sustainability by favoring social inclusion and equity, through easier access to services and facilities by foot, bicycle or public transport, and encouraging people meet each other by face-to -face interactions (Williams 1999; Bramley and Power 2009; Arbury 2006).
As Neuman (2005) pointed out, this thesis was claimed not only by scientists but also by important institutions, such as the Urban Land Institute (1998), the American Planning Association (1999), the European Environment Agency (1998), and the United Nations (1992). This generated a wide consensus around the importance to plan more compact cities, particularly in Europe, the United States, and Australia.
An effective synthesis of main socio-economic and environmental goals linked to high-density environments emerging from several planning documents has been proposed by Churchman (1999). These relate to the following spheres: environmental quality, transportation systems, physical infrastructure and urban form, social factors, and economic factors.
Recent Urban Planning Movements and Theories Advocating the Compact City Model
During the 1990s, the ideal of the “compact city” inspired real movements that have been initially developed and further codified in the Anglo-Saxon countries, where the suburban development was born (Reale 2008).
The US smart growth movement, endorsed by the US Environmental Protection Agency (EPA), was born with the aim of preserving open spaces and parkland and protecting critical ecosystems form urban sprawl. The main principles were to improve low-carbon transportation choices (walking, bicycling, and transit), to promote brownfield redevelopment and imperviousness reduction, and to develop better higher density housing (Smart Growth Network 2006; Danielsen et al. 1999). A branch of the Smart Growth movement is the New Urbanism, whose theorization has been generally attributed to Duany and Plater-Zyberk (1991) and advocated in the USA as a response to urban sprawl. The New Urbanism approach seeks to achieve compact, liveable, pedestrian friendly, and mixed-use neighborhoods (CUN 1999) by giving a strong importance to a human-scaled urban master design (Neuman 2005). The New Urbanism design proposal is based upon adapting the design principles of “traditional” towns to the modern life style, integrating walkable communities with a strong local identity. The urban structure is strongly based on a Transit-Oriented Development, an urban planning model theorized by the New Urbanist Peter Calthorpe (1993), which tends to intensify the presence of residential, business uses, leisure, and facilities within a walking distance of public transport nodes, to drastically reduce the need of car.
These movements of architects and urban planners arrived to define real densification techniques of existing settlements, by producing handbooks and guidelines where urban planning and design techniques specific for achieving compact and mixed-use settlements have been punctually codified.
In Europe the compact city has been deeply investigated especially in the British literature, where several scientists wrote extensively on the topic. Intensification theories and policies investigated in the British context were focused on maximizing the use of urban land, with the redevelopment of existing buildings, vacant and derelict land, the intensification of activities in order to preserve the countryside and open spaces in urban areas (Jenks et al. 1996).
A valuable contribution was provided by the Urban Task Force led by Richard Rogers who advocated the idea of a well-designed, compact, and connected city designed around its public spaces (Urban Task Force 1999). The city is conceived as not in contradiction with the aim of ensuring good life conditions and wellbeing. The sustainable city model proposed by Rogers is characterized by few key elements: compactness and polycentric structure, good connections based on public transport, walking and cycling, mixed-use urban environments, socially mixed, environmentally responsible, well-designed urban environment, and technologically advanced. By undertaking such a compact city model, Rogers puts on the agenda the priority need to upgrade the existing urban fabric and to use the derelict and brownfield sites before developing greenfield.
New Challenges for the Compact City: Further Evolution of the Concept
As already stressed, the compact city concept has gained a wide consensus during the final part of the last century, evolving from a simple urban containment policy to protect the natural environment and agricultural land, to a multipurpose policy that includes sustainability principles (OECD 2012). This leads to the proposition of specific strategies and targets aimed at preserving land and consequently at intensifying the existing city. As a matter of fact, in Europe specific targets for limiting land take and promoting compactness have been introduced by the European Commission within the EU Environment Action Programme to 2020 (seventh EAP) which aims to have policies in place by 2020 in order to achieve “no net land take” by 2050 in each Member State.
However, while the drive towards the promotion of more compact cities became strong, several studies have expressed some concerns about its potential to de facto ensure urban sustainability (Breheny 1992, 1996; Stretton 1996; Gordon and Richardson 1997; Mindali et al. 2004; Jenks and Burgess 2000; Williams et al. 2000; Neuman 2005). The predicted benefits due to the implementation of compact city policies were not happening as they were foreseen, and the effects were not in line with economic environmental and social demands (Thomas and Cousins 1996).
Compact urban forms and urban density have reflected complex and multifaceted issues that should have been carefully managed and assessed to ensure liveability, health, and wellbeing of the urban environment, as well as to reduce CO2 emissions and energy consumption in cities. Moreover, new challenges have been identified in the framework of urban sustainability, such as urban resilience and climate change adaptation, which require open permeable spaces and greener solutions. Indeed, exceeding in increasing the urban density could determine not only the increase of traffic congestion, air and noise pollution, and GHG emissions but also the lack of necessary green spaces and permeable soils for limiting the UHI effects and the risks due to the occurrence of ordinary and extreme weather events, such as floods or heatwaves.
Consequently, the debate of these last few years has focused on the conflicting balance between a just containment of land take and optimal compactness that ensures minimum levels of urban green spaces. As a matter of fact, the loss of green space and arable land and the deterioration of ecosystems are concerns for both developed and developing countries, since by 2030 two-thirds of the world’s population will be living in cities, the urban population in developing countries will double, and the area covered by cities could triple (Un-Habitat 2016). At the same time cities’ request of open green spaces and higher quality of life seems constantly increasing (OECD 2012).
Therefore, the challenge today is to constantly assess not only that intensification processes are aimed at regenerating existing urban fabrics, providing cites with necessary services and amenities, but also that the compact city model is liveable, e.g., that ensures optimal climate conditions, liveability, public health, and good functioning of existing urban systems and infrastructures (Conticelli et al. 2017).
With the SDG11 the 2030 Urban Agenda clearly recognizes the importance to promote more compact settlements. Indeed, the SDG11 stresses the need of a more efficient use of land considered as able to better provide and manage public services (water, transport, waste) at a lower cost and to consume less energy than dispersed settlements. This position gives new attention to the positive effects of more compact settlements, encouraging further investigations on understanding what are the key features of compact cities and the importance to define optimal values on what constitutes an efficient land use and indicators to measure it.
Key Features of Compact Cities
Measuring Urban Compactness
Measuring density and compactness is a typical task planner do to calculate specific requirements of urban services, to estimate site capacities, and to control urban development on specific sites.
Dwelling unit density, the number of dwellings within a standard spatial unit, which is commonly used at city scale for estimating the housing needs and as reference unit by the real estate market. It is also an important parameter for estimating the minimum legal requirements of public facilities and services, such as water and sewer pipes, roads, and electricity to buildings.
Population density, the number of people within a standard spatial unit, which is commonly used by technicians for establishing the urban load of a new development and then for sizing infrastructural networks and systems. Indeed, population density is an appropriate indicator of potential transit use, to make such service viable. Population density may also provide information about urban vitality: high population density can enhance social interactions due to proximity. A similar parameter frequently used together population density is the employment density, measuring the number of jobs in any given area.
Floor area density expressed in floor area ratio (FAR) and also known as Plot Ratio and Floor Space Index – which is the ratio of the number of square meters (feet) of floor space in buildings to the square meters (feet) of the property or lot. It is commonly used at the parcel scale, is very useful for studying the link between density and urban form, and is strongly oriented to the project.
All of these measures may be either net or gross: net density is calculated within a development site and excludes roads, parks, and other nonresidential land uses; gross density includes all land uses within a given area incorporating the broader network of public spaces.
Although these are common measures of the same entity, they provide different information; therefore, it is important to look at all the three numbers to obtain a detailed picture of density for a given area. In fact, the relationship between population, dwelling unit, and floor area densities depends on household size and crowding.
Moreover, at a wider scale, residential density based on the extent of the total amount of urbanized areas can give interesting information of what city expansion is going on. In fact, it registers the relationship between city expansion and population growth.
Density is a quantitative indicator, therefore is very useful in describing the urban form in quantitative terms, while its usefulness to capture the qualitative characteristics is limited. Indeed, it does not control the building height; thus, it is quite possible to build high-rise low-density or low-rise high-density.
In this sense density should be considered in conjunction with other indicators describing the urban form. An additional indicator completing density is the coverage, which is the ratio of the ground floor area of enclosed buildings to the area of the lot. Developments with the same FAR may have very different coverage, thus producing different urban environments in terms of building heights and open spaces.
The OECD (2012) proposes additional indicators for describing urban compactness as well as densification policies. One parameter is proximity, concerning how urban functions are sprawled in a metropolitan area. It measures how much one urban activity is close to another in a metropolitan area, thus being applied both to monocentric and polycentric settlements. Proximity can be measured by analyzing the average transport distances due to commuting as well as to shopping and leisure and by mapping land cover data, to estimate how much land is used for urban purposes.
Other indicators are related with the presence public transport systems which are necessary to underpin high urban densities. They can be expressed in terms of share of trips using public transport in total trips, or share of population and/or employment within a given walkable distance to public transport stops in total population.
Another key parameter describing urban compactness is the mix of use, most widely used to indicate accessibility to local services and jobs, but less frequently considered and measured by urban planners. In literature mixed land use concept has not a unique meaning and finding proper indicators is a challenge. Burton (2002) identified three main indicators describing the mix of uses: varied and plentiful supply of facilities and services, showing the provision of public facilities and the balance between residential and nonresidential land uses; horizontal mix of uses, describing the geographical distribution of different uses throughout the city; vertical mix of uses, referring the mix of uses within single buildings.
Techniques and Tools for Increasing Urban Compactness
Pursuing a compact city model implies to undertake a process of making existing cities denser, encouraging more people to live in urban areas, and building at higher densities. This means to intensify cities. The term “urban intensification” is commonly related with processes that make an area more compact. It is also compared with “urban consolidation” an alternative term describing the same intensification and compaction processes, frequently used in Australian literature.
Land-use planning and zoning are cities’ primary tools for increasing urban density. Land-use planning has the role of ordering and regulating land use in an efficient and sustainable way. Governments use land-use planning to manage the development of land within their jurisdictions by planning for the needs of the community while safeguarding natural resources. By doing so land-use planning typically encompasses zoning which regulates the types of activities that can be accommodated on a given piece of land, as well as the amount of space devoted to those activities, and the ways that buildings may be situated and shaped.
Within this framework, specific tools can be identified as mainly dedicated to increase urban compactness. These can be grouped in two main categories: planning and incentive-based tools.
Planning and Design Tools
Two main techniques applied for intensify existing urban developments are “infilling” and “redevelopment.” Both techniques are aimed at increase not only the urban density but also the mix of uses of the entire neighborhood.
Infilling consists in small urban interventions on an already developed lot aimed at adding more units and regenerating the existing urban fabrics. Although this is the most obvious strategy to increase urban density, it faces many obstacles, due to the lack of empty infill sites and the opposite need to preserve and ensure green open spaces within the city.
Urban redevelopment occurs when a built-up area is totally replaced with new buildings and open spaces. In general, it happens in existing urban areas, which are underutilized or abandoned, or in brownfields and often involves a rezoning by the local government, representing a chance to build high-density buildings or urban attractors (mixed-use or commercial) thus increasing the overall density of the neighborhood. It is frequently accompanied by a provision of infrastructure improvements (mass transit, such as metro lines) that can support such up-zoning.
There are additional intensification techniques affecting the density but with no particular effects on the urban form: e.g., the increase of the number of housing units due to the division of large dwelling, and the rehabilitation of vacant or underused buildings. The former influences the possibility to host an increased number of people in a given area and the latter ensues a maximization of the use of built up assets.
Dying malls, strip malls and enclosed malls
Postwar suburban system of thoroughfares (the highway, the arterial, the collector, the local and the cul-de-sac) which are transformed into complete, multimodal streets
Huge and empty parking lots, which are resized and redeveloped with the introduction of new functions
Conventional single-use zoning, made of single-family houses, which are retrofitted through a rezoning creating a hierarchy of public spaces and new urban functions
Additional measures encouraging urban density are incentive-based tools. One example is represented by density bonuses, widely used in the United States. They allow developers to increase the maximum allowable development on a site than that normally permitted in exchange for either funds or in-kind support for specified public policy goals, such as affordable housing, additional public facilities and spaces, as well as environmental conservation. This tool works best in cities in which market demand is strong and land availability limited.
Another measure is the transfer of building rights. Development rights generally refer to the maximum amount of floor area permissible on a given lot. When the actual built floor area is less than the maximum permitted floor area, the difference is referred to as “unused development rights,” municipalities can dispose (and transfer) to engage in more intensive land development (Amirtahmasebi et al. 2016). This tool is mainly applied as an incentive to intensifying cities thus avoiding urban sprawl. Landowners in peri-urban and suburban areas are encouraged to sell their development rights to private developers, realizing an economic return. Developers, in turn, have an interest in building increased density in urban areas where there is strong market demand.
The compact city concept has evolved over time showing to be rather controversial for achieving sustainable development because there still remain many questions surrounding exactly how compact the compact city should be. However, it has been a reference model in urban planning since the very beginning of the discipline and even before. In fact, there is no city without compactness.
Two main ways of defining what is city have been identified at global level in the framework of the SDG work (UN-Habitat 2018). They are clearly based on city compactness and density. The former considers the urban extent, i.e., the contiguous area occupied by buildings and other impervious surfaces, which is measured in terms of extent of built-up sites within a given area thus generating three main classes: urban built-up areas, suburban built-up areas, and rural built-up areas. The latter defines cities against their degree of urbanization, which is expressed in terms of population size, density, and contiguity of settlements. This classification distinguishes three settlement types: densely, intermediate, and thinly populated areas.
Moreover, the Sustainable Development Goals recognize the compact city as a good model to make cities and human settlement inclusive, safe, resilient, and sustainable. Indeed the SDG11 considers reducing urban sprawl as one of the actions through which achieving sustainable cities and communities. This will inevitably be an important worldwide reference in the compact city debate for the forthcoming decades.
- Arbury J (2006) From urban sprawl to compact city – an analysis of urban growth management in Auckland. University of Auckland, AucklandGoogle Scholar
- Breheny MJ (1992) The contradictions of the compact city: a review. In: Breheny MJ (ed) Sustainable development and urban form. Pion Ltd., London, pp 138–159Google Scholar
- Breheny MJ (1996) Centrists, decentrists and compromisers: views on the future of urban form. In: Jenks M, Burton E, Williams K (eds) The compact city: a sustainable urban form? E & FN Spon, London, pp 13–35Google Scholar
- Burgess R (2000) The compact city debate: a global perspective. In: Jenks M, Burgess R (eds) Compact cities. Sustainable urban forms for developing countries. Spon Press, London, pp 9–24Google Scholar
- Burton E, Jenks M, Williams K (eds) (2000) Achieving sustainable urban form. E & FN Spon, LondonGoogle Scholar
- Calthorpe P (1993) The next American metropolis: ecology, community and the American dream. Princeton Architectural Press, New YorkGoogle Scholar
- Commission of the European Communities (CEC) (1990) Green paper on the urban environment. European Commission, BrusselsGoogle Scholar
- Congress for the New Urbanism (CUN) (1999) Charter of the new urbanism. McGraw-Hill, New YorkGoogle Scholar
- Duany A, Plater-Zyberk E (1991) Towns and town-making principles. Rizzoli International, New YorkGoogle Scholar
- Dunham-Jones E, Williamson J (2009) Retrofitting suburbia. Urban design solutions for redesigning suburbs. Wiley, HobokenGoogle Scholar
- Jacobs J (1961) The death and life of great American cities. Random House, New YorkGoogle Scholar
- Jenks M, Burgess R (eds) (2000) Compact cities. Sustainable urban forms for developing countries. Spon Press, LondonGoogle Scholar
- Jenks M, Jones C (eds) (2010) Dimensions of the sustainable city. Springer, Dordrecht/Heidelberg/London/New YorkGoogle Scholar
- Jenks M, Burton E, Williams K (eds) (1996) The compact city: a sustainable urban form? E & FN Spon, LondonGoogle Scholar
- Mindali O, Raveh A, Salomon I (2004) Urban density and energy consumption: a new look at old statistics. Transp Res A 38:143–162Google Scholar
- Newman P (1992) The compact city: an Australian perspective. Built Environ 18(4):285–300Google Scholar
- Reale L (2008) Densità, città, residenza. Tecniche di densificazione e strategie anti-sprawl [Density, city, housing. densification techniques and no-sprowl strategies], Gangemi, RomeGoogle Scholar
- Smart Growth Network (2006) This is smart growth. https://www.epa.gov/sites/production/files/2014-04/documents/this-is-smart-growth.pdf. Accessed 6 May 2018
- Stretton H (1996) Density, efficient and equality in Australian cities. In: Jenks M, Burton E, Williams K (eds) The compact city: a sustainable urban form? E & FN Spon, London, pp 37–43Google Scholar
- Tachieva G (2010) Sprawl repair manual. Island Press, Washington, DCGoogle Scholar
- Thomas L, Cousins W (1996) The compact city: a successful, desirable and achievable urban form? In: Jenks M, Burton E, Williams K (eds) The compact city: a sustainable urban form? E & FN Spon, London, pp 53–65Google Scholar
- UN-Habitat (2016) Urbanization and development: emerging futures. World cities report 2016. United Nations Human Settlements Programme (UN-Habitat), NairobiGoogle Scholar
- UN-Habitat (2018) Tracking progress towards inclusive, safe, resilient and sustainable cities and human settlements. SDG 11 synthesis report high level political forum 2018. United Nations Human Settlements Programme (UN-Habitat), NairobiGoogle Scholar
- Urban Task Force (1999) Towards an urban renaissance. Spon, LondonGoogle Scholar
- Williams K, Burton E, Jenks M (eds) (2000) Achieving sustainable urban form, E & FN Spon, LondonGoogle Scholar
- World Commission on Environment and Development (WCED) (1987) Our common future. Oxford University Press, OxfordGoogle Scholar