As people flock to cities around the world in search of work and a better life, municipal authorities are struggling to meet rising demand for housing, jobs, transport, healthcare, food and water.
That challenge is made even harder by the stresses of climate change, which is bringing more extreme weather, from floods to heat waves, and higher sea levels that threaten coastal cities.
The result is that migrants from rural areas - especially in developing countries – often end up in slums, now home to nearly 1 billion people across the world, where many live in poverty.
There is a growing recognition that if cities are to become more resilient to disaster threats and better able to serve their residents, they need to understand what is happening in slums, experts told a Zilient discussion on the issue this week.
Who is living in a city's slums, in what conditions, and what are their needs? These are questions on which many government officials draw a blank, said Skye Dobson, director of learning, monitoring and evaluation for Slum Dwellers International (SDI), a global network of organisations working in informal settlements.
"We are seeing now that in debates around resilience, the issues of informality and inequality are coming up very strongly - but yet there's not really sufficient data to address this in the resilience planning of cities," Dobson told the Zilient webinar, which showcased new projects hoping to change this situation.
A campaign called Know Your City, run by SDI, the Cities Alliance global partnership and United Cities and Local Governments of Africa, is collaborating with the Global Infrastructure Basel (GIB) Foundation to apply its SmartScan tool that assesses – and seeks to improve – infrastructure projects.
It measures projects against 75 criteria on sustainability and resilience in informal settlements, from environmental performance to human rights and transparency
Combined with data collected by slum communities using the SDI system, a pilot in Durban will build evidence about the best ways to upgrade more than 20 slums, and feed that into the South African city's wider resilience strategy.
"Information is power," said Ndodeni Dengo, regional coordinator with South Africa's Informal Settlement Network (ISN).
He described how his informal neighbourhood of Kwa-Mathambo in a Durban suburb had undertaken a "reblocking" exercise, to rebuild and redesign its streets after a major fire in 2016.
As part of that, the community worked with the authorities to plan the layout of new water and sanitation facilities including stand pipes and toilets, ensuring they were safe for women and children. The city also provided electricity.
"The municipal authorities started to negotiate with us," said Dengo, adding that data collected by the slum dwellers served as a "power tool" - even in terms of the city being able to find out how many people actually live there.
Before that process, the 800 or so inhabitants of Kwa-Mathambo were like "dogs in kennels" compared to the formal residential areas nearby, Dengo said. "Now when we go out, our neighbours are recognising us - they know we are human beings."
Similar work of profiling and mapping slums, and gathering statistics about the occupants and their lives, has been done by slum communities in about 225 cities in Africa and Asia - with the ultimate aim of enabling cities to use that data to develop in a more resilient and inclusive way.
Another project working to that end in Africa involves integrating SDI’s Know Your City data into the process of crafting a broader resilience strategy for Accra in Ghana and South Africa’s Cape Town, which are both members of the 100 Resilient Cities (100RC) network, backed by The Rockefeller Foundation.
Nse Esema, a programme manager with 100RC, said summaries of slum data and recommendations based on the data are being developed for local governments and their resilience officers in the two cities.
"African cities and others in the global south can't ignore the informal sector - both because we believe it constitutes such a significant portion of the city and because of the inherent strengths within the sector that can be leveraged in the resilience-building process," Esema told the discussion.
The project in Cape Town, for example, is looking at which economic sectors are vibrant in slums, and could be supported by the city to provide more employment for local people, she said.
Alhassan Baba Fuseini, national data coordinator of the Ghana Federation of the Urban Poor, said the process of gathering data in Accra has enabled community members - including a large proportion of women - to share their experiences, "break out" the issues they are facing, and come up with relevant and sustainable ways of solving them, in partnership with the city authorities.
"It is working well for us," he said.
Esema of 100RC said it was important to find ways of making this kind of collaboration a lasting process that does not depend on personal connections, and can continue to function on a long-term basis.
ISN's Dengo noted that data on slums "is the key to open all doors at the municipality level".
But efforts can't stop with the provision of data - valuable as that is to cities that may have little information about their slums, said SDI's Dobson.
"Data alone isn't what is making the change," she explained. The next step is for communities to organise themselves and turn the data they gather into a plan or strategy that can make a real difference to their lives.
Katharina Schneider-Roos, chief executive officer of the GIB Foundation, said the SmartScan tool can help inhabitants of informal settlements use their data to identify priorities for improving infrastructure and turn those into a business case that could attract private investors.
She noted World Economic Forum estimates that infrastructure in developing countries accounts for "the vast majority of the required finance" needed to meet the U.N. Sustainable Development Goals, aimed at ending poverty and hunger by 2030, among other ambitions.
Much of the funding to pay for slum upgrades has so far come from the public purse, as well as community funds and savings groups, said Dobson. "To date, we haven't fully understood how to engage the private sector," she said.
The hope is that if the slum data projects now being supported by the Resilience Measurement, Evidence & Learning Community of Practice, a network of more than 180 specialists, with grants from The Rockefeller Foundation, prove successful in amplifying slum dwellers’ voices at the city level, that may soon start to change.