Box Story: Is Density Destiny? Making Density Work for Cities

Background

Many cities around the world have the advantage of being part of larger countries which extend beyond the limits of their city boundaries, allowing them to move certain infrastructure or land uses out to suburban areas. For instance, New York City’s water supply is sourced from a 5,180-km² watershed located upstate, with some sections being up to 200 km away from the city. Commuter towns have also developed around cities like Melbourne, and their residents make the daily trip into the city for work. In contrast, as an island city-state, Singapore has little choice but to accommodate all its needs within its limited land.

Over the past 20 years, Singapore’s population density has increased to 8,207 persons per km². Although the city continues to explore new approaches to increase its capacity through land reclamation and in more recent years, underground planning, there are inherent constraints to these strategies.

Singapore is not the exception and as the pace of urbanisation intensifies globally, other cities will also become increasingly denser. In contrast, some cities will grapple with depopulation, sometimes affecting multiple cities within the same country. However, built-up cities often evoke images of concrete jungles and over-crowdedness. Density is also typically associated with urban challenges such as congestion, housing inaccessibility, greater crime risk, social isolation, and an overall strain on the city’s infrastructure. A high concentration of residents in any one area amplifies the demand for urban services like healthcare, transportation and essential utilities. This in turn may lead to a rising cost of living and social tensions.

Despite the conventional view that urban density erodes liveability, there are cities that have bucked the trend and are able to mitigate the negative impacts of high-density living. In 2024, CLC updated its Liveability Matrix by plotting metropolitan population densities against total liveability scores from the Economist Intelligence Unit’s (EIU’s) Global Liveability Index. These scores focus on five categories: Stability, Healthcare, Culture and Environment, Education, and Infrastructure.

The CLC Liveability Matrix plots cities’ population densities against liveability scores; Singapore is one of a few high-density cities that scored well in EIU’s Global Liveability Index 2023 (Centre for Liveable Cities)

The resulting Matrix showed that Singapore was one of a few high-density cities that came out ahead in the EIU rankings. Other dense cities in the survey that were identified as more liveable included Hong Kong, Barcelona and London. These cities have undertaken a variety of strategies to manage urban density while balancing liveability outcomes.

Dealing with Density Creatively

For built-up cities that deal with mostly brownfield developments, it is crucial to ensure that each parcel of land is used optimally. This calls for long-term planning to anticipate future needs, as well as innovation to make the most of available space. Besides building higher, planners can optimise land use by adopting atypical strategies such as building underground, constructing over water, and utilising air rights.

A notable example is Hong Kong, which has made significant strides in leveraging the potential of underground space. Despite spanning 1,100 km², only about 25% of the city’s land area has been developed due to its hilly terrain.19 This means that the actual population density is much higher than the city-wide average of 6,900 persons per km². To free up surface land for more human-centric activities, Hong Kong has put infrastructure like utilities and emergency facilities underground. The city also turned its challenging geology into an advantage through its 2016 Cavern Master Plan, which identified multiple sites that could accommodate new uses including data centres, warehouses and columbariums.

In addition to maximising land, it is equally important for planners of high-density cities to keep residents in mind and design human-centric environments that do not feel overcrowded. One way is to integrate nature into the city. This not only helps to visually break up the urban fabric, but it also provides respite to city dwellers and offers space for social interaction. A study by the Nanyang Technological University has shown that vertical greenery is also able to act as stress buffers in cities. Additionally, landscaping delivers environmental benefits, such as combatting the urban heat island effect which dense cities are prone to. With many other competing uses within a city, planning for green and blue spaces cannot be an afterthought. Instead, these considerations need to be incorporated upstream such as through zoning decisions, designation of green belts and building controls.

Singapore is a city that has prioritised the provision of pervasive greenery, which is central to its goal of becoming a City in Nature. On top of conserved nature reserves, nature areas, parks and park connectors, pockets of vegetation can be found along pavements, road dividers and sheltered walkways. Overcoming the pressures of land scarcity, Singapore also emphasises skyrise greenery where plants are incorporated onto rooftops and vertical spaces. This is facilitated through urban design guidelines and green building certification requirements. There are also initiatives like the Landscaping for Urban Spaces and High-Rises programme which promotes the replacement of greenery lost due to development with vertical plantings, as well as the Skyrise Greenery Incentive Scheme which co-funds installation of eligible projects. This softens harsh building façades and contributes to Singapore’s green cover of around 40%.

Even with these measures in place, dense cities will continue to grapple with the effects of heavy traffic and pollution. Hence, cities should make a paradigm shift towards sustainable urban systems that enable more efficient use of resources and reduce the generation of negative externalities. For example, cities that have attained a higher public transport modal share are able to move more commuters over longer distances, producing lower levels of carbon emissions with fewer cars on the road. Accordingly for cities like Tokyo and Hong Kong that have been growing their rail networks, there has been a decreasing trend of emissions arising from the transport sector. Cities can also deploy district-level infrastructure like cooling and pneumatic waste collection systems which can capitalise on the economies of scale of densely populated areas, while minimising disamenities like noise and visual clutter.

Barcelona has the highest car density of any city in the European Union at about 6,000 per km², leading to concerns regarding air quality, safety and congestion. To address this, the city pioneered the concept of combining nine blocks into one “Superblock” (Superilla) and transforming the roads within into pedestrian-priority streets. Building on this urban structure, Barcelona is also creating Green Streets which will be scaled up to distribute benefits linearly across the city through traffic calming, greening and new public spaces. There have been concrete improvements to liveability as a result of these efforts. For instance, traffic in the Sant Antoni Superblock dropped by 17% on average and localised pollution decreased by 40%. Researchers have also estimated that the Barcelona Superblocks could generate further benefits to health, including the prevention of almost 700 deaths annually and an increased life expectancy of about 200 days among residents.

Rooftop greenery in Singapore (Unsplash)

Cities are complex systems where each person acts as an individual agent who interacts with other people and the environment in different and unpredictable ways. As cities become denser, this complexity is further compounded. Planners and policymakers must consider the interplay among these various components. Technology is a powerful tool that can support both the management of services and infrastructure as well as better decision-making. Examples of applications range from installing sensors to track real-time data to having digital platforms for residents to report municipal issues, enabling more informed responses to the challenges that dense cities face.

This can be seen in the case of London, where an interactive virtual reality digital twin of the Square Mile was designed. Covering 2.9 km² of the financial district, this innovative technology aims to assist developers and city officials in visualising how a project could affect its surroundings by mapping detailed features like lamp posts and windows to an accuracy of 2 cm. Such capabilities are especially valuable in dense cities to optimise space and simulate scenarios without impacting existing operations. Moreover, the digital twin translates technical plans into simpler models for stakeholder consultations. The city has continued to ramp up its investments in this aspect and has also produced digital twins to guide climate mitigation initiatives.

Every city has its unique set of circumstances, considerations and priorities. These strategies showcase how there are diverse approaches to ensuring liveability in high-density settings. With the right planning and governance to alleviate adverse effects, a high concentration of people can also boost vibrancy in cities.

When Density Works

In Triumph of the City, leading economist Edward Glaeser noted that “cities speed innovation by connecting their smart inhabitants to each other”. He argues that this is true for developed cities in the Western part of the world but even more so for emerging markets. Indeed, with compact and heavily populated areas, close proximity encourages collaboration and the sharing of ideas. Dense cities are thus likely to evolve into economic gateways that attract global talent. Alongside that, density cultivates cultural diversity as people bring their distinctive traditions, customs and practices with them to new places.

These qualities are reflected in the Global Power City Index (GPCI) by the Institute for Urban Strategies at the Mori Memorial Foundation. The GPCI evaluates 48 cities in terms of their magnetism, or “power to attract people, capital, and enterprises from around the world”. Looking at Hong Kong, Singapore, Barcelona and London, the four cities fall within the top half of the overall ranks in the 2024 edition of the index. Specifically, they excel in measures such as World’s Top Universities (Hong Kong ranked 2^nd), International Freight Flows (Singapore ranked 3^rd), Number of International Conferences (Barcelona ranked 7^th) and Number of International Students (London ranked 1^st).

However, these outcomes are only possible because the cities have established a firm grasp on dealing with their density-associated challenges, while also seizing the potential positives. As urbanisation intensifies globally, the need to reshape density from an obstacle to an engine for sustainable growth and liveability will become even more pertinent, and cross-learning from cities that have worked well with density can only benefit all.

Superblocks are about 400 m by 400 m each, and have been implemented in neighbourhoods across Barcelona (Unsplash)