The spread of the coronavirus has placed urban density in the dock of international public opinion.

The Covid-19 pandemic has reactivated concerns about the negative effects of high population densities in cities. The World Health Organisation's (WHO) advice to reduce the spread of the virus by "maintaining physical distances and avoidance of close, unprotected contact" would lead us to assume that densely populated cities are dangerous places.

New York Governor Andrew Cuomo added substantial weight to this assumption when he tweeted that "NYC must develop an immediate plan to reduce density" to combat future pandemics - garnering 26,000 likes. Commentator Joel Kotkin added to the anti-density mood by suggesting that the low-density "sprawl (of Los Angeles) may have saved lives" (Los Angeles Times). Both received support of a more scientific kind from Stanford University epidemiologist Steven Goodman, who proclaimed density to be "an enemy" (The New York Times).

Mr Cuomo, Mr Kotkin, Dr Goodman and other commentators are not saying anything new. They are restating a set of ideas concerning city design that date back to the 19th century at least. At that time, old European cities with high densities and narrow street networks were thought to intensify the threat of diseases like cholera and typhoid.

In response, modernist architects and city planners began advocating for reduced city densities. They designed aerated cities with lower densities, improved hygiene, access to light, air and potable water, as well as proper plumbing. They were also built around automobility, the use of cars as the main mode of transport.

This meant greater distances between buildings, wider streets and avenues, and homes individually equipped with clean and efficient kitchens and bathrooms. This modernist approach was eagerly adopted across the world and guided the reconstruction of war-torn cities and the construction of brand new cities in the second half of the 20th century.

Singapore, of course, not only inherited this modernist approach to city planning, but also energetically innovated upon it in a host of ways. Most importantly, Singapore planners re-injected the values of density to modernism. The economic successes of Singapore and other cities in East Asia helped the world rediscover the benefits of density.

Today, urban designers, planners and related policy experts - from Singapore's Urban Redevelopment Authority and Housing Board, as well as the United Nations and the World Bank - regard high densities as a fundamental principle for sustainable and vibrant cities.

Density, according to this new consensus, offers benefits such as the convenience of diverse and co-located services, the clustering of complementary jobs, the energy efficiencies of proximate consumers and reduction of travel demand, and the intensification of urban experience.

For economists, higher density means better market integration. Furthermore, scholars increasingly recognise that high-density cities can help curb urban sprawl, thereby reducing competition for food-producing hinterlands.

In short, urban density offers the best opportunity to harness economies of scale and agglomeration, while bringing a host of social, cultural and environmental benefits, and aligning with wider issues of food security.

It is no surprise that advocates of urban density are working hard to challenge the link between urban density and high rates of Covid-19 infection. The World Bank, for example, correlated recent data on Covid-19 cases and population in Chinese cities and concluded that "urban density is not an enemy in the coronavirus fight".

Unfortunately, other evidence clouds the situation. It is reassuring to know that there are high-density cities where incidences have been comparatively low (Hong Kong, Taipei, Shanghai). Yet, comparably high infection numbers can be observed at opposite ends of the density spectrum. Hyper-dense neighbourhoods such as Dharavi in Mumbai (Patranabis, Gandhi and Tandel, 2020) and relatively low-density regions of rural Africa, for example, are both witnessing a high number of cases, according to the WHO.

What is clear is that density, as a single quantitative measure, tells us little about the incidence of Covid-19.

What seems to count is how density is designed - that is, integrated with other factors. Cities are complex assemblages of people, activities, institutions, regulations, information, knowledge, capital, spaces, buildings, technology, infrastructure, parks, gardens and waterways. Good cities are those that weave all of these elements together.

Hong Kong, Taipei and Shanghai unlock the benefits of density because they do that well, while in hyper-dense Dharavi and low-density rural Africa many such city elements are either unavailable or inadequate.

Redesigning the Singapore city

What does this emerging debate mean for Singapore and the post-coronavirus world? There are four action points that jump out.

FIRST, DEEPEN DENSITY INTEGRATION

Singapore already integrates density into the city well. Density is never just a number, but is used as a parameter around which transport, energy, water and waste infrastructures are planned. Jobs, services and amenities are arranged in ways that make neighbourhoods convenient, liveable and, in some older cases, lovable.

Not all densities are equal, however. A matter of weeks ago, Singapore was regularly cited in the international press as an exemplary high-density, low coronavirus-incidence city. This all changed with the virus outbreak in the foreign worker dormitories.

Suddenly, it seemed, two densities were revealed to be coexisting awkwardly in one city. While those densities were likely to be comparable in quantitative terms, they were starkly different in qualitative ones.

So, the urgent issue is to deepen the integration of density so that all residents benefit.

SECOND, INTENSIFY USE OF THE OUTDOORS

Recent studies show that Covid-19 cases in China occurred predominantly indoors, in homes and workplaces and on public transport. Comparatively few cases were contracted outdoors.

By comparison to the Northern Hemisphere where winters can be harsh, Singapore benefits from a relatively benign climate. It is true that the heat and humidity of the tropics can be a challenge. But conducting more of our everyday life outside - or at least in sheltered but not confined spaces - is feasible.

Singapore's hawker centres point the way. Other forms of dining, as well as exercise, worship, entertainment and even classes and business meetings, could be enhanced with outdoor aspects. These activities can be supported by rapid advances in low-energy outdoor cooling technology, passive cooling principles for public space design, better cycling infrastructure and expansion of the tradition of outdoor gymnasiums. These initiatives fit hand-in-glove with broader efforts to integrate nature into the city.

THIRD, DIVERSIFY MOBILITY

Commuting remains a weak spot for Covid-19 transmission in dense cities around the world. The rise in shared, electric and potentially autonomous mobility offers some exciting opportunities to reduce reliance on mass-transit buses and private cars for commuting.

This could increase choice for commuters. More interesting still is the possibility to bring goods and services to individual homes and communities. Design studies are already being conducted in this area, with a focus on how on-demand or highly flexible schedules could work. Pop-up markets and the FairPrice on Wheels initiative are useful examples.

FINALLY, DESIGN THE 'CYBER-PHYSICAL' CITY

This means integrating virtual and augmented technologies (cyber) with the ordinary spaces of everyday life (physical). Think of the Zoom or Skype video calls that we make with increasing regularity in this circuit breaker period. Add to this communication on Twitter, Facebook, Instagram and other social media platforms as well as integrated sensor systems, and we start to approach a mixed cyber-physical city. Designing the cyber-physical city presents enormous challenges, such as in ensuring data privacy, handling fake news and managing the stresses that come from mixing domestic and professional activities in compact homes. New flexible live-work designs will be needed along with deeper integration of virtual technologies.

The benefits of urban density are well known and will not become irrelevant overnight. Density alone is not enough, however. Complex assemblages like cities require density to be designed.

Density must be woven into the city fabric, so that its benefits are harnessed for all in a post-coronavirus world.

• Stephen Cairns is director of the Future Cities Laboratory, Singapore-ETH Centre, a collaboration between the National Research Foundation and ETH Zurich, a Zurich-based university specialising in technology, engineering and mathematics.