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A literature review and analysis is presented on the influence that urban density has on the diffusion of Covid-19. Six main categories of factors are identified: urban settlement, socioeconomic factors, urban services, urban environment, policies and time. At this stage there is no scientific consensus about the effect of density. Urban connectivity appears to play a bigger role in the diffusion of the pandemic. Important gaps are identified in the literature on the compared governance of risk and the density at the building level. More research should be directed to the evaluation of adaptation measures adopted by cities, communities and individuals. The relation between urban density and health issues should be framed in a vulnerability perspective, considering the interplay between exposure, sensitivity and the adaptive capacity of cities.Policy relevanceGiven the lack of consensus between scientific studies, it is too early to reverse the existing policies and recommendations that promote dense and compact development. Instead, more attention should be paid to the types/conditions of density and the equitable access to urban services and green infrastructures in order to minimise risks and lower the burden of social-distancing measures in dense environments. Resilience policies should focus on addressing deficiencies in the existing urban environment that are at the core of the epidemic outbreak. These policies should be based on a close collaboration with local communities and intermediate actors (e.g. planners, architects, health officials, etc.) to address social, economic and technological inequalities.

Population growth and land use change often have significant environmental impacts, affecting biodiversity, water supply, agricultural production, and other resources. Future scenario models can provide a better understanding of these changes, helping planners and the public understand the consequences of choices regarding development density, land use, and conservation. This study presents a model that has been used to identify alternative future scenarios for Florida considering future population growth and land use. It includes two scenarios: a “Sprawl” scenario reflecting a continuation of current development patterns and a “Conservation” scenario with higher densities, redevelopment, and more land protection. The study incorporates sea level rise scenarios for both 2040 and 2070. Results show that the Sprawl scenario could lead to 3.5 million acres of new developed land and 1.8 million acres of lost agricultural land by 2070 in Florida. In contrast, the Conservation scenario for 2070 results in 1.3 million fewer acres of developed land and 5 million more acres of protected natural land, showing that it is possible to accommodate future population growth while reducing impacts to agricultural and conservation priorities in Florida. Although this is by no means a “prediction” of future Florida, it has been useful as a tool for evaluating potential future land use scenarios and is a model that may be more broadly applied by other locations and users.

This paper examines the influence of public greenspace on the life satisfaction of residents of Australia's capital cities. A positive relationship is found between the percentage of public greenspace in a resident's local area and their self-reported life satisfaction, on average corresponding to an implicit willingness-to-pay of $1172 in annual household income for a 1 per cent (143 square metres) increase in public greenspace. Additional results suggest that the value of greenspace increases with population density and that lone parents and the less educated benefit to a greater extent from the provision of public greenspace than the general population. In all, these results support existing evidence that public greenspace is welfare enhancing for urban residents and adequate allowance should be made for its provision when planning urban areas.

Empirical research establishing the costs and benefits that can be associated with polycentric urban systems is often called for but rather thin on the ground. In part, this is due to the persistence of what appear to be two analytically distinct approaches in understanding and measuring polycentricity: a morphological approach centring on nodal features and a functional approach focused on the relations between centres. Informed by the oft-overlooked but rich heritage of urban systems research, this paper presents a general theoretical framework that links both approaches and discusses the way both can be measured and compared in a coherent manner. Using the Netherlands as a test case, it is demonstrated that most regions tend to be more morphologically polycentric than functionally polycentric. The difference is largely explained by the size, external connectivity and degree of self-sufficiency of a region's principal centre.

Despite growing recognition of the important role of cities in economic, political and environmental systems across the world, comparative, global-scale research on cities is severely limited. This paper examines the similarities and differences in urban form and growth that have occurred across 25 mid-sized cities from different geographical settings and levels of economic development. The results reveal four city types: low-growth cities with modest rates of infilling; high-growth cities with rapid, fragmented development; expansive-growth cities with extensive dispersion at low population densities; and frantic-growth cities with extraordinary land conversion rates at high population densities. Although all 25 cities are expanding, the results suggest that cities outside the US do not exhibit the dispersed spatial forms characteristic of American urban sprawl.

East-Southeast Asia is currently one of the fastest urbanizing regions in the world, with countries such as China climbing from 20 to 50% urbanized in just a few decades. By 2050, these countries are projected to add 1 billion people, with 90% of that growth occurring in cities. This population shift parallels an equally astounding amount of built-up land expansion. However, spatially-and temporally-detailed information on regional-scale changes in urban land or population distribution do not exist; previous efforts have been either sample-based, focused on one country, or drawn conclusions from datasets with substantial temporal spatial mismatch and variability in urban definitions. Using consistent methodology, satellite imagery and census data for >1000 agglomerations in the East-Southeast Asian region, we show that urban land increased >22% between 2000 and 2010 (from 155 000 to 189 000 km2), an amount equivalent to the area of Taiwan, while urban populations climbed >31% (from 738 to 969 million). Although urban land expanded at unprecedented rates, urban populations grew more rapidly, resulting in increasing densities for the majority of urban agglomerations, including those in both more developed (Japan, South Korea) and industrializing nations (China, Vietnam, Indonesia). This result contrasts previous sample-based studies, which conclude that cities are universally declining in density. The patterns and rates of change uncovered by these datasets provide a unique record of the massive urban transition currently underway in East-Southeast Asia that is impacting local-regional climate, pollution levels, water quality availability, arable land, as well as the livelihoods and vulnerability of populations in the region.

Living organisms generally occur at the highest population density in the most suitable habitat. Therefore, invasion of and adaptation to novel habitats imply a gradual increase in population density, from that at or below what was found in the ancestral habitat to a density that may reach higher levels in the novel habitat following adaptation to that habitat. We tested this prediction of invasion biology by analyzing data on population density of breeding birds in their ancestral rural habitats and in matched nearby urban habitats that have been colonized recently across a continental latitudinal gradient. We estimated population density in the two types of habitats using extensive point census bird counts, and we obtained information on the year of urbanization when population density in urban habitats reached levels higher than that of the ancestral rural habitat from published records and estimates by experienced ornithologists. Both the difference in population density between urban and rural habitats and the year of urbanization were significantly repeatable when analyzing multiple populations of the same species across Europe. Population density was on average 30 % higher in urban than in rural habitats, although density reached as much as 100-fold higher in urban habitats in some species. Invasive urban bird species that colonized urban environments over a long period achieved the largest increases in population density compared to their ancestral rural habitats. This was independent of whether species were anciently or recently urbanized, providing a unique cross-validation of timing of urban invasions. These results suggest that successful invasion of urban habitats was associated with gradual adaptation to these habitats as shown by a significant increase in population density in urban habitats over time.

Achieving sustainable urban development amid rapid urbanization requires a deep understanding of how urban density influences human well-being. This study examines the spatial relationship between built-up population density (BUD) and human well-being across Delhi, one of the world’s fastest-growing megacities. Using a combination of high-resolution census data, remote sensing, and spatial analysis, the study identifies markedly uneven urban form characterized by extreme density variation, ranging from 2,884 to 136,385 persons per km² across clusters, and uncoordinated development, particularly in peripheral zones. While BUD significantly affects well-being outcomes, the analysis reveals that beyond an optimal threshold, socio-economic conditions become equally influential. The findings emphasize the urgent need for differential planning strategies: promoting infrastructure and planned densification in low-density peripheries; encouraging mixed-use development in moderate-density zones; and alleviating congestion while enhancing services in high-density, unplanned areas. These insights provide a policy framework aligned with the Sustainable Development Goals, particularly Goal 11, which aims to make cities inclusive, safe, resilient, and sustainable. By emphasizing the spatial heterogeneity of urban density and its implications for well-being, this research provides a valuable lens for urban policy and planning in rapidly growing global cities.

Do higher urban densities contribute to more sustainable cities and communities? This paper examines the effectiveness of higher density (as a means) for achieving sustainable urban development (the goal) following three lines of enquiry. First, a systematic review of the scientific literature (n = 229 peer-reviewed empirical studies) is presented on the effects of urban density. Second, the motivations for increasing urban density are studied in a systematic review of Swedish planning practices based on the comprehensive urban plans in 59 municipalities. Third, these two studies are compared to find matches and mismatches between evidence and practice. Although positive effects exist for public infrastructure, transport and economics, there are also considerable negative environmental, social and health impacts. This creates a challenging task for urban planners to assess the trade-offs involving densification and accommodate current urbanisation rates. Some topics are found to be over-represented in research (transport effects), seldom discussed in practice (environmental impact), and misaligned when comparing motives and evidence (social impact). Furthermore, for some topics, urban density thresholds are found that are important because they may explain some of the divergences in the results between studies.Practice relevanceThe transfer of knowledge from research to planning practice is a serious concern as planning strategies are not aligned with scientific evidence. Planning practice in Sweden is more positive about the contribution of higher density to sustainable urban development than the results of empirical studies warrant. The largest deviation is found in relation to the social impacts of higher density where the planning arguments are not aligned with the evidence. Several reported negative effects of densification (e.g. water management, recreational infrastructure, biodiversity) are not sufficiently accounted for in Sweden’s planning policy and strategy. The narrow planning focus on decarbonising cities and densification needs to be broadened to ensure cities are resilient against the effects of climate change and include mitigation strategies to reduce negative social, environmental and health impacts. The findings can be used to develop evidence-based planning strategies. Other countries can apply this process to assess their planning strategies.