In recent decades, the world has experienced unprecedented urban growth. In 2015, close to 4 billion people — 54 per cent of the world’s population — lived in cities and that number is projected to increase to about 5 billion people by 2030. Rapid urbanization has brought enormous challenges, including growing numbers of slum dwellers, increased air pollution, inadequate basic services and infrastructure, and unplanned urban sprawl, which also make cities more vulnerable to disasters. Better urban planning and management are needed to make the world’s urban spaces more inclusive, safe, resilient and sustainable. As of May 2017, 149 countries were developing national-level urban policies.

• The proportion of the urban population that lives in developing country slums fell from 39 per cent in 2000 to 30 per cent in 2014. Despite some gains, the absolute number of urban residents who live in slums continued to grow, owing in part to accelerating urbanization, population growth and lack of appropriate land and housing policies. In 2014, an estimated 880 million urban residents lived in slum conditions, compared to 792 million urban residents in 2000.
• As more and more people move to urban areas, cities typically expand their geographic boundaries to accommodate new inhabitants. From 2000 to 2015, in all regions of the world, the expansion of urban land outpaced the growth of urban populations. As a result, cities are becoming less dense as they grow, with unplanned urban sprawl challenging more sustainable patterns of urban development.
• The safe removal and management of solid waste represents one of the most vital urban environmental services. Uncollected solid waste blocks drains, causes flooding and may lead to the spread of water-borne diseases. On the basis of data from cities in 101 countries from 2009 to 2013, 65 per cent of the urban population was served by municipal waste collection.
• Air pollution is a major environmental health risk. In 2014, 9 of 10 people who live in cities were breathing air that did not comply with the safety standard set by WHO.

Source: Report of the Secretary-General, "Progress towards the Sustainable Development Goals", E/2017/66

Many cities around the world are facing acute challenges in managing rapid urbanization— from ensuring adequate housing and infrastructure to support growing populations, to confronting the environmental impact of urban sprawl, to reducing vulnerability to disasters.

• Between 2000 and 2014, the proportion of the global urban population living in slums dropped from 28.4 per cent to 22.8 per cent. However, the actual number of people living in slums increased from 807 million to 883 million.
• Based on data collected for 214 cities/municipalities, about three quarters of municipal solid waste generated is collected.
• In 2016, 91 per cent of the urban population worldwide were breathing air that did not meet the World Health Organization air quality guidelines value for particulate matter (PM 2.5); more than half were exposed to air pollution levels at least 2.5 times higher than that safety standard. In 2016, an estimated 4.2 million people died as a result of high levels of ambient air pollution.
• From 1990 to 2013, almost 90 per cent of deaths attributed to internationally reported disasters occurred in low- and middle-income countries. Reported damage to housing attributed to disasters shows a statistically significant rise from 1990 onwards.

Source: Report of the Secretary-General, The Sustainable Development Goals Report 2018

Substantial progress has been made in reducing the proportion of the global urban population living in slums, though more than 1 billion people continue to live in such situations. Urgent action is needed to reverse the current situation, which sees the vast majority of urban residents breathing poor-quality air and having limited access to transport and open public spaces. With the areas occupied by cities growing faster than their populations, there are profound repercussions for sustainability.

• Between 1990 and 2016, the proportion of the global urban population living in slums fell from 46 to 23 per cent. This progress was largely offset by internal population growth and rural-urban migration. In 2016, just over 1 billion people lived in slums or informal settlements, with over half (589 million) living in East, South-East, Central and South Asia.
• The proportion of urban residents who have convenient access to public transport (defined as living within 500 m walking distance of a bus stop and within 1,000 m of a railway and/or ferry terminal) remains low, particularly in developing countries. Based on data from 227 cities from 78 countries in 2018, on average, 53 per cent of urban residents in all regions had convenient access to public transport, from a low of 18 per cent in sub-Saharan Africa to a high of 75 per cent in Australia and New Zealand. In some regions that have low access to public transport, informal transport modes are highly prevalent and in many cases provide reliable transport for the majority of urban populations.
• Globally, urban areas are expanding at a faster rate than their populations. Between 2000 and 2014, areas occupied by cities grew 1.28 times faster than their populations. Closely related to this trend is that the urban densities of cities have been declining, creating profound repercussions for environmental sustainability at the local, regional and global scale. Better management of urban growth will be crucial in order to guarantee sustainable urbanization.
• Globally, 2 billion people do not have access to waste collection services and 3 billion people lack access to controlled waste disposal facilities. With increasing urban populations and the existence of consumer-oriented economies amid rising income levels and rapid urbanization, it is estimated that the total waste generated in the world will double from nearly 2 billion tons in 2016 to about 4 billion tons by 2050. While from 2010 to 2018 the proportion of solid waste collected was about 81 per cent globally, in sub-Saharan Africa it was only 52 per cent.
• In 2016, 9 in 10 people living in urban areas still breathed air that did not meet the World Health Organization’s air quality guidelines value for particulate matter – that particulate matter 2.5 microns or less in size (PM2.5) not exceed an annual mean of 10 micrograms per m3 or a daily mean of 25 micrograms per m3 – and more than half of the world population experienced an increase in PM2.5 from 2010 to 2016.
• Most cities have struggled to ensure that their populations have convenient access to open public spaces (defined as spaces within 400 m walking distance of their residence). Based on data from 220 cities in 77 countries in 2018, only 21 per cent of the population had convenient access to open public spaces. However, these results do not necessarily mean that there is an inadequate share of land dedicated to open public spaces in these cities, but rather that their distribution across urban areas is uneven.
• National urban policies are policy strategies that specifically respond to the urbanization challenges of today. As of the beginning of 2019, 150 countries had developed such policies, and almost half are already implementing them.

Source: Report of the Secretary-General, Special edition: progress towards the Sustainable Development Goals

• More than half the world’s population lives in cities. By 2030, it is projected that 6 out of 10 people will be urban dwellers. Despite numerous planning challenges, well-managed cities and other human settlements can be incubators for innovation and ingenuity and key drivers of sustainable development.
• However, as more people migrate to cities in search of a better life and urban populations grow, housing issues intensify. Already in 2014, 30 per cent of the urban population lived in slum-like conditions; in sub-Saharan Africa, the proportion was 55 per cent, the highest of any region. Globally, more than 880 million people were living in slums in 2014. This estimate does not include people in inadequate or unaffordable housing (defined as costing more than 30 per cent of total monthly household income).
• As population growth outpaces available land, cities expand far beyond their formal administrative boundaries. This urban sprawl can be seen in many cities around the world, and not only in developing regions. From 2000 to 2015, the ratio of the land consumption rate to the population growth rate in Eastern Asia and the Oceania was the highest in the world, with developed regions second. Other regions, such as South-Eastern Asia and Latin America and the Caribbean, showed a decrease in that indicator over the same time period. Unfortunately, a low value for this ratio is not necessarily an indication that urban dwellers are faring well, as this can indicate a prevalence of overcrowded slums. Unplanned urban sprawl undermines other determinants of sustainable development. For example, for every 10 per cent increase in sprawl, there is a 5.7 per cent increase in per capita carbon dioxide emissions and a 9.6 per cent increase in per capita hazardous pollution. This illustrates the important interlinkages across the goals and targets.
• Likewise, managing solid waste is often problematic in densely populated areas. In fact, in many developing regions, less than half of solid waste is safely disposed of. As per capita waste generation continues to rise, the collection and safe disposal of solid waste will continue to require serious attention.
• Urban air pollution also challenged cities around the world, causing illness and millions of premature deaths annually. In 2014, around half the global urban population was exposed to air pollution levels at least 2.5 times higher than maximum standards set by the World Health Organization.
• The quest for sustainable and coordinated urban development starts with national policies and regional development plans. As of 2015, 142 countries had a national urban policy in place or under development. Those countries are home to 75 per cent of the world’s urban population.