In the process of urbanization，large cities with dense population and complex social networks are faced with potential public security risks due to environmental pollution，dramatic climate change and other factors. Under the background of urbanization and globalization，the spreading scope and speed of infectious diseases in large cities have further increased. The emergence of new infectious diseases such as influenza A（H1N1），SARS，avian influenza，and the recent outbreak of Corona Virus Disease 2019（COVID-19），have posed serious threats to public safety and major challenges to public health and urban planning.

For coping with the severe public health problems caused by infectious diseases，scholars began to study the relationship between urban space environment and public health in combination with disciplines such as Environmental Health，Public Health and Epidemiology. As a result，the discipline of Modern Urban Planning with health as its appeal has come into being. In the field of Geography and Urban Planning，studies on the prevention and control of infectious diseases mainly include studies on public health management，public policies，infectious disease surveillance and evaluation，quality management in grassroots community，etc. Scholars in such fields have been continuously expanding the application of GIS in the studies of infectious disease prevention and control，mainly including infectious disease surveillance，analyses on the spatial distribution of infectious diseases，analyses on the influence of environmental space factors and other aspects.

The scholars have pointed out that public health can be safeguarded by improving the disaster and epidemic prevention capability in urban public transport system，completing the urban public health management system，and incorporating the epidemic prevention planning into urban planning for disaster prevention and reduction The COVID-19 outbreak has once again raised thinking about how urban planning prevents and controls diseases in terms of space governance. From the perspective of urban planning，it is necessary to sort out the challenges faced by large cities with high public risks when in respond to the epidemic，and propose corresponding planning interventions to enhance the ability to cope with public risks，so as to exert positive effects of urban planning in improving public health，and to achieve the organic integration of Public Health and Urban Planning disciplines.

Globally，patients with COVID-19 were mostly concentrated in large cities，significantly more than in rural areas. Compared with small cities and rural areas，once the outbreak occurs in large cities，the spread of the epidemic is stronger and its negative impact is greater. The main characteristics of large cities affected by infectious diseases are as follows：

（1）Fast diffusion

Infectious diseases such as COVID-19 mainly spread through the air and social networks. In this dynamic system，large cities are nodes in the entire infectious disease transmission network，which increases the contacts among contagious pathogens，vectors and susceptible population，providing an opportunity for the outbreak and resulting in serious public health consequences. In large cities with developed transportation and high population density，people are more likely to be exposed to the viruses. Hence，population mobility and urban spatial structure affect the spreading speed and scope of epidemic diseases. Compared with rural areas and small cities，transport networks in large cities are more developed，epidemic prevention and control is more difficult，and infectious diseases are more widespread. Once an infectious disease occurs，it is often hard to control.

（2）Greater harm

In large cities with developed economy，highly concentrated population and overloaded environmental carrying capacity lead to the shortage of land，water and medical resources，exposing urban public security to severe challenges. Due to overpopulation，medical and health resources in large cities are also under tremendous pressure when faced with public health emergencies. Once there are infectious diseases in large cities，fast diffusion，one of the characteristics，can lead to a surge of infection number in large cities in the short term，which will cause a huge impact on the urban medical and healthcare system；in addition，the epidemic will quickly spread in the short run，causing serious public health consequences. Due to the pivotal role of large cities in social and economic life，the epidemic can not only cause harm to the health security of citizens in large cities，but also give rise to significant losses to the regional economy under shutdown.

When in the outbreaks，urban spatial systems in large cities face the following challenges：

（1）High-density urban spatial structure easily causes the rapid spread of epidemics

Urban population density and traffic development affect the spreading scope and speed of infectious diseases. The spread of infectious diseases is mainly through social networks，so it is influenced by factors such as population mobility，geospatial location，etc. In the process of urban development，with the increasing urban population and the continuous expansion of urban scale，intensively developing land resources makes the spatial distribution pattern of central areas in large cities too dense. Besides，populations from various cities and countries gather in urban central areas and move frequently. They all increase the risk of the epidemic spreading. The larger the urban scale is and the more complex the urban network structure is，the faster the virus spreads. If an outbreak is found in a highly concentrated central location，it will be difficult to control. Therefore，how to optimize the overall spatial layout structure of a city and improve the prevention capacity of urban space in response to an outbreak，is the first key issue to be considered in the current urban planning.

（2）Public facilities spatial layout planning lacks the consideration of public health security

Disease outbreaks have led to a severe impact on the urban medical and healthcare system，exposing the shortcomings of the existing medical resources in cities when responding to major public health events. In addition to medical facilities，buildings with large public spaces，such as stadiums，can also play an important role in epidemic prevention and control. At present，the planning of public service facilities in most cities is generally divided the planning area into multiple various planning units that are configured with corresponding medical，cultural，and educational infrastructures. As it is difficult to allocate the public facilities resources in each independent unit uniformly，there is still a lack of adequate preparation and awareness when dealing with major public security problems caused by infectious diseases ^[15].

（3）Emergency capacity of urban basic living space for epidemic prevention and control needs to be improved

In the aspect of planning，the past blueprint planning has failed to meet the growing demands for health. Disease outbreaks have enabled us to realize the importance of urban space governance. To improve the capacity for space governance，it is necessary to improve the urban emergency capacity responding to the epidemic. Community，as the unit of urban basic living space，is an important line for epidemic prevention and control. The COVID-19 outbreak has revealed some problems in the community’s prevention and control of infectious diseases：The communities in large cities are densely populated，and their residential areas are mostly high-rise housing. Potential security risks brought by the public ventilation system make high-density housing prone to cross infection；Supporting infrastructures are difficult to meet all the needs in residential areas，thus it is hard to guarantee life supplies and life security；Community sanitation conditions need to be improved，such as garbage disposal，sewage treatment and other potential health and security concerns. Seen in this light，improving the epidemic prevention capacity of urban basic living space units，and optimizing community space environment，have become another challenge in the future urban planning.

（4）There is a contradiction between the high mobility of public transport system and the traffic control under epidemic prevention and control

During the prevention and control of infectious diseases，urban transport network system has played a significant role. On the one hand，epidemic prevention and control needs to decrease the mobility of urban traffic. Blocking the traffic in the hardest hit areas is an effective way to prevent virus spreading. These traffic control measures were vital to protect residents’ health，but at the same time also restricted the daily travel of residents. In the mid to late period of the outbreak，as the epidemic situation gradually improved，various walks of life began to resume production and operation，and the travel demand of urban residents grew rapidly，hence the public transport was under great pressure. How to satisfy the daily travel needs of urban residents while reducing public health risks brought by the complex public transport networks，has become a major challenge for traffic management and planning departments. On the other hand，transportation has played a crucial part in emergency supplies delivery and personnel treatment. The allocation of medical resources and the emergency supplies for residents both depend on transport system. Therefore，from the perspective of urban disaster and epidemic prevention，how to improve the urban public transport system and carry out emergency transport planning has become a key content to consider in the future planning.

With regard to the prevention and control of infectious diseases，the following attempts can be made in urban spatial planning：

（1）Develop decentralized and clustered urban spatial structures，and set up Sanitary Protection Zones

The spread of infectious diseases is closely related to urban space and social network structure. The disordered spread of large cities leads to the complex spatial network structure，which makes it difficult to carry out unified control over the entire urban space，and poses challenges to epidemic prevention and control. Therefore，it is of necessity to consider the needs for epidemic prevention in the overall urban planning layout，to change the single thinking mode of expansionary planning in the past，and to think about how to optimize the urban spatial structure in the light of decentralization and isolation. It is suggested to develop decentralized and clustered urban spatial structures that enable land layout，population and employment to be comparatively decentralized through space separation. Once an outbreak occurs，each cluster can operate independently，which can reduce the pressure of the entire urban spatial systems when faced with public health emergencies.

Meanwhile，it is recommended to set up Sanitary Protection Zones between clusters and functional areas to prevent the spread of diseases. Judging from the characteristics of COVID-19 outbreak，novel coronavirus can also spread by aerosol. The resistance and absorption of urban green space can reduce the security risks brought by infectious diseases，playing a role of sanitary isolation to a certain extent. Accordingly，it is advised to increase the urban green space whose proportion is strictly controlled，and to improve the capability of green space for disaster and risk prevention by adding some emergency support and auxiliary facilities.

（2）Rationally allocate urban public space resources，and carry out prevention and emergency planning

For relieving the pressure of urban medical and healthcare system caused by the COVID-19 outbreak，many cities have reconstructed mobile cabin hospitals with utilizing the existing buildings with large public spaces，such as stadiums and schools，to reasonably allocate the idle public spaces due to the outbreak. To some degree，it has made up for the deficiency of existing medical space resources in cities. The spatial layout planning of urban public facilities should not only satisfy the needs of daily lives，but also focus on the serious public security risks brought by epidemics and the disasters. Therefore，it is significant to comprehensively distribute the urban space resources for epidemic prevention，and to develop the vital role of public space resources in disaster and epidemic prevention.

It is suggested that from the perspective of space，the potential health risks in addition to the disaster and risk prevention capability of the existing urban public infrastructures，can be comprehensively analyzed and evaluated，besides，can be graded and ranked according to the above capacity. Through the development of corresponding reconstruction and new construction measures or spatial layout optimization，carry out prevention and emergency planning，so as to enable public space to play positive roles in public health，and meanwhile，to improve the emergency capacity of urban public space. In terms of spatial layout，it is proposed to reserve urban White Space as lands for emergency in cities. The reserved sites for epidemic prevention facilities should be as far as possible located downwind of the dominant wind direction，and far away from population gathering areas and water bodies in city centers，to avoid the impact of passive site selection after outbreaks.

（3）Optimize the layout structure of various functional facilities，and improve the ventilation，lighting and sanitation conditions in communities

Community，as the unit of urban basic living space，is an important front for epidemic prevention and control. Since this outbreak，the government has introduced the closed-off community management，which was an important measure to control the epidemic，and has achieved remarkable results，slowing down the spread of the outbreak. However，the epidemic prevention capacity is still to be improved. Considering that community has exerted crucial role in epidemic prevention and control，it is necessary to conduct scientific governance on the unit of urban basic living space from the planning level，and to strengthen the epidemic prevention power of grassroots communities.

In planning respect，it is recommended to take the improvement of disaster and epidemic prevention capacity as the basic requirement，to optimize the layout structure of various functional facilities，and to improve the ventilation，lighting and sanitation conditions in communities，for satisfying the requirements in resident daily life and basic epidemic prevention. Evaluate the air ventilation of community buildings；formulate the evaluation criteria of community wind environment；moderately transform the building space that does not meet the requirements of epidemic prevention. As for the building layout，strictly control building intervals；plan ventilation corridors；improve the overall ventilation environment and lighting conditions in communities. Garbage stations should be arranged in the area with good ventilation conditions；additional sanitary protection facilities should be installed，and the disinfection treatment should be carried out regularly. Promote the construction of intelligent and healthy communities；manage and monitor the everyday wellness of residents by building information technology network platforms；report the health data in order to provide timely treatment and emergency plans.

（4）Improve urban public transport network spaces，and plan to set up emergency channels

The population mobility under the influence of urban transport networks has affected the spreading scope and speed of infectious diseases. Transport networks has been significant in the control of epidemic spreading，the allocation of medical resources，the delivery of emergency supplies，etc. Therefore，regarding to the control of epidemic spreading，it is possible to greatly reduce the risk of infection with contagious virus，by means of optimizing urban public transport networks and reducing population gathering and mobility to block the spread of virus. It is suggested to increase the spatial planning and design of Slow Traffic System and advocate the green travel mode.

In terms of emergency traffic planning，strengthen studies on emergency traffic guarantee；consider the requirements of disaster and epidemic prevention in planning and design；improve the emergency capacity of transport system. It is recommended to set up emergency accesses for epidemic prevention（such as special channels for the delivery and allocation of emergency supplies，emergency rescue channels，etc.），to form network architectures within regional units，and to control by regions，in order to provide transport support for public health emergencies.

（Translated by Li Zhiqing）