Exploring the association of population density with urban livability
Optimizing population density has been recognized as an important way to improve urban livability,which is also the ultimate goal that human society has been pursuing.Although many disciplines,such as geo-graphy,urban planning,psychology,economics,and ecology,have made some explorations on the relation-ship between population density and urban livability,none of the existing theories among these disciplines have directly and systematically introduced the relationship between population density and urban livability.Moreover,the existing theories are mainly based on low-density contexts,ignoring high-density contexts in East Asia,especially in China,leading to relatively limited applications of these theories.This paper takes Chinese and American cities as examples,which are proxies of high-and low-density contexts,respectively.By comparing the research findings in these contexts,we aim to seek a generalized relationship between popu-lation density and urban livability.After reviewing the current empirical evidence,we found that population density has an important impact on urban livability but its impacts differ between Chinese and American cities.First,in American cities,population density has positive associations with commuting durations.A possible reason is that a higher population density reduces distances to destinations and improves accessibility to facilit-ies.However,Chinese cities provide opposite evidence,which shows that population density has a negative re-lationship with commuting durations.This may be because a higher population density in China often induces traffic congestion.Second,population density is mainly negatively related to air pollution in American cities,whereas it is mainly positively associated with air pollution in Chinese cities.Third,many American studies suggest that population density has a positive relationship with physical health,because a higher population density promotes active travel,leading to higher levels of physical activity.However,studies from Chinese cit-ies show that population density has negative or inverted U-shaped associations with physical health due to limited space for physical activity.Fourthly,population density has positive associations with subjective well-being by enhancing social capital in American cities,whereas it is negatively associated with subjective well-being by reducing social capital in Chinese cities.An important explanation for the above differences is that the basis of population is different between the U.S.and China.That is,population density may have different ef-fects on urban livability in low density contexts(i.e.,American cities)and high density contexts(i.e.,Chinese cities).Combining both contexts,we conclude that there is an inverted U-shaped law between population dens-ity and urban livability.In particular,in the low-density contexts,a higher population density promotes urban livability,because it is conducive to reducing travel duration,improving air quality,and enhancing citizens'physical health and subjective well-being.However,in high-density contexts,a higher population density tends to reduce urban livability,as it may prolong travel duration,worsen air quality,and decrease citizens'physical health and subjective well-being.This inverted U-shaped relationship between population density and urban livability reminds geographers and urban planners to reconsider the local contexts of population density when designing and building livable and sustainable cities in China and other countries all over the world.
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