Seeing the city through data

Researchers found that calls to prayer in Riyadh cause dips in mobile phone usage throughout the city. Image: Getty.

This is an edited extract from Decoding the City, a collection of writing on data-driven urbanism from MIT's SENSEable City Lab. This piece examines how data can be used to map residents’ activity in cities, and how the resulting analysis can be used to guide transport policy and even map residents' cultural, religious and social activities. 

In early 2007, a group of Google Earth users made a curious discovery in San Diego. Panning across the newly available satellite imagery, the armchair Magellans noticed a set of structures that formed an inexplicable shape when viewed from above; a Nazi swastika.

The find went viral – well before the concept of going viral existed – and was picked up by major news outlets. It was quickly discovered that the complex, whose surrounding roadways are coincidentally named after WWII-related sites, was actually built in 1967 by the US Navy.

Now visible to anyone with an Internet connection, the base’s plan view caused great public outcry, and the resulting political pressure led to a $600,000 reconstruction project to unmake the abhorrent shape. “We don’t want to be associated with something as symbolic and hateful as a swastika,” a spokesperson said.

The Navy claims the exact form and orientation of the structure was wholly unintentional, and simply the consequence of a humiliating planning oversight. But whether deliberate or not, it’s clear the project’s planners, architects, and builders were not anticipating a god’s-eye-view perspective on the finished project.

As ridiculous as the whole episode was, it highlights a particularly powerful idea: New ways of seeing can drastically refigure our understanding of, and relationship to, place.

Of course, not all urban data sets are as intrinsically visual as satellite imagery. Many require the context of urban spatiality to understand and operationalize them – i.e., they gain salience and power when seen through the city. The de facto example of this power – thanks in large part to Edward Tufte’s proselytization– is on display in John Snow’s 1854 cholera outbreak map :

Basic germ theory had not yet been accepted by the medical field, but by mapping cholera deaths across Soho, Snow was able to tangibly communicate the idea that cholera was transmitted not through infected air, but rather through contaminated water and food.

Now, in an age where data is everywhere, the prevailing notion is that important stories sit somewhere within all data, and consequently, the task of analysis and representation is to simply uncover these stories. And thus, the march toward data-absolutism continues, instilling a tendency to cast meaning where it simply doesn’t exist – to identify or construct false patterns in the great static that is big data.

What does this all mean in the context of the city? On a fundamental level it underscores the fact that urban datasets are powerful and capricious; they encapsulate countless dimensions at myriad physical and temporal scales, and a wide gulf exists between possible relationships and actionable results. Our struggle is now in reclaiming a sense of legitimate, verifiable meaning from the morass, i.e., reorienting our processes of modeling, simulation, and representation to distill value while also keeping validity in check.

The following project, in which we attempted to understand transport patterns in the Saudi Arabian city of Riyadh, illustrates our approach to achieving this delicate balance.

An urban traffic system for the city of Riyadh

Rapid economic and demographic changes throughout Saudi Arabia are posing new challenges and opportunities for the Kingdom. Of particular concern is the explosive growth of the nation’s capital, Riyadh, where development is quickly outpacing transportation infrastructure - between 1987 and 1995, automobile trips increased at the rate of 9 percent per year.

The Urban Traffic System project aims to develop an innovative, highly dynamic urban traffic system to address the mobility challenges specific to the city.  To this end, the project is based on creating an alternative to traditional intelligent transportation systems by taking advantage of the digital traces of our everyday lives – specifically, mobile phone usage -  to create models for mobility analysis, intervention, and planning, for policy makers, planners, and development professionals, as well as for the citizens of Riyadh themselves.

We partnered with telecom companies in the region to collect roughly one month of total phone activity across the country, where mobile phone penetration is, astonishingly, over 198 per cent. We aggregated nearly 100 million daily network connections, assigned to more than 10,000 unique cell towers.

Seeing Riyadh through Data

This image shows mobile phone activity through color, transparency, and height across Riyadh. This visualisation projects strong portrait of the social character of the city. With the inclusion of satellite imagery as a base map, we arrive at a unique view of how the social rhythm of the city is expressed over built form.

Watching the oscillations of the activity landscape, a unique character emerges – we see that the city really doesn’t come alive before noon, and peaks in aggregate activity around 6.15 pm. With a careful eye, we can begin to pick out subtle regional delineation: the residential neighborhoods to the south-west and northeast of the downtown core activate well before the rest of the city, and experience the strongest interhour fluctuations throughout the course of the day.

By overlaying our results on the geography of the city, a number of interesting relationships are revealed. Most strikingly, the clusters correlate very closely with the main arteries of the city. Mobility communities seem to be heavily reliant on the street network itself, underscoring the city’s overall dependence on highway infrastructure.

From the planning perspective, one of the most meaningful stories we can glean from this data is an how an individual moves through the city, which, at an aggregate level, describes one of the most vital components of urban analysis: origin-destination matrices. Traditionally, O-Ds, which are vital for transport network optimisation, are constructed through onerous census surveys that are conducted every five to ten years. The process is long and costly, and when completed, only provides a rudimentary snapshot of travel demand.

By collecting and filtering each user’s mobile activity, however, we are able to estimate a population’s travel demand in terms of origins and destinations of individual trips. We’ve shown that these approximated O-D flows hold a strong correlation to census estimates; however, this approach includes the added benefit of capturing travel demand which includes seasonal variations and hourly fluctuations.

What next?

Returning to John Snow’s cholera map, are we able to reveal hidden facets of social life by affixing our data to the structure of the city? And consequently, what can this transposition further teach us about the character and composition of urban form in Saudi Arabia?

One cultural phenomenon that is unique to the Arab world is the daily call to prayer. While collecting our data, we found an intriguing pattern in mobile activity distributions that was unlike any other country or city we’ve analyzed before: at various points in the day activity would simply drop off for around thirty to forty minutes before picking back up to its typical trend. These inactivity “valleys” were actually the result of these daily prayer times.

Millions of Muslims across the country put down their phones to turn and face the holy city of Mecca to give prayer five times a day. Shops and businesses essentially close down for roughly twenty to thirty minutes while the religious police – the Mutaween – surveil the streets in the hopes of sending all loiterers to the nearest mosques. To our surprise, our activity distributions very closely capture this behaviour.

 The timing of these calls to prayer depend on the position of the sun in the sky, and thus, by looking at western, central, and eastern regions, we are able to see the prayer times moving across the country.. This presents another series of intriguing questions.

This sudden dip in cellular activity is identifiable when applied to the geography, but can we quantify and map the intensity of the disruption and show which areas are most affected by calls to prayer? Does it follow the density distribution of mosques? Leading from this, can we detect and illustrate how prayer time disruptions are expressed through mobility? Do average trip lengths shorten during prayer windows? Lastly, can the intensity of disruption serve as a proxy for regional religiosity?

We will continue forward with all of these questions in mind. And through this careful, back and forth negotiation into and away from the spatial frame, we hope to arrive at a collection of representations that capture new ways of seeing both the city and the social forces operating there.

Decoding the City is edited by Dietmar Offenhuber and Carlo Ratti and was released by Birkhauser in August. 


How China's growing cities are adapting to pressures on housing and transport

Shenzhen, southern China's major financial centre. (Photo by Daniel Berehulak/Getty Images)

In the last 40 years, the world’s most populous country has urbanised at a rate unprecedented in human history. China now has over 100 cities with populations greater than a million people, easily overshadowing the combined total of such cities in North America and Europe. 

That means urban policy in China is of increasing relevance to planning professionals around the world, and for many in Western nations there’s a lot to learn about the big-picture trends happening there, especially as local and national governments grapple with the coronavirus crisis. 

Can Chinese policymakers fully incorporate the hundreds of millions of rural-to-urban migrants living semi-legally in China’s cities into the economic boom that has transformed the lives of so many of their fellow citizens? The air quality in many major cities is still extremely poor, and lung cancer and other respiratory ailments are a persistent threat to health. Relatedly, now that car ownership is normalised among the urban middle classes, where are they going to put all these newly minted private automobiles?

Yan Song is the director of the University of North Carolina, Chapel Hill’s Program on Chinese Cities and a professor in the school’s celebrated urban planning department. She’s studied Chinese, American, and European cities for almost 20 years and I spoke with her about the issues above as well as changing attitudes towards cycling and displacement caused by urban renewal. This conversation has been edited for length and clarity.

American cities face very different challenges depending on which part of the country they are in. The Rust Belt struggles with vacancy, depopulation, and loss of tax base. In coastal cities housing affordability is a huge problem. How do the challenges of Chinese cities vary by region?

Generally speaking, the cities that are richer, usually on the eastern coastal line, are facing different challenges than cities in the western "hinterland." The cities that are at a more advantaged stage, where socio-economic development is pretty good, those cities are pretty much aware of the sustainability issue. They're keen on addressing things like green cities.

But the biggest challenge they face is housing affordability. Cities like Beijing, Shanghai, Shenzhen, and Hangzhou are trying to keep or attract young talent, but the housing prices are really, really high. The second challenge is equity. How do you provide equal, or at least fair, services to both the urban residents and the migrants who are living in the city, to alleviate some of the concerns around what the government is calling “social harmony?” 

Then the cities in the hinterland, typically they are resource economies. They are shrinking cities; they're trying to keep population. At the same time, they are addressing environmental issues, because they were overly relying on the natural endowments of their resources in the past decades, and now they're facing how to make the next stage of economic transition. That's the biggest divide in terms of regional challenges.

These urban centers rely on migrant workers for a lot of essential services, food preparation, driving, cleaning. But they live tenuous lives and don't have access to a lot of public services like education, health care, social insurance. Are Chinese policymakers trying to adopt a healthier relationship with this vast workforce?

The governments are making huge efforts in providing basic services to the migrants living in the city. They're relaxing restrictions for educational enrollment for migrants in the cities. In health care as well as the social security they are reforming the system to allow the free transfer of social benefits or credits across where they live and where they work [so they can be used in their rural hometown or the cities where they live and work]. 

In terms of health care, it's tough for the urban residents as well just because of the general shortage of the public health care system. So, it's tough for the urban residents and even tougher for the migrants. But the new policy agenda's strategists are aware of those disadvantages that urban migrants are facing in the cities and they're trying to fix the problem.

What about in terms of housing?

The rental market has been relaxed a lot in recent years to allow for more affordable accommodation of rural-to-urban migrants. Welfare housing, subsidised housing, unfortunately, skews to the urban residents. It's not opened up yet for the migrants. 

The rental market wasn't that active in previous years. But recently some policies allow for more flexible rental arrangements, allowing for shared rentals, making choices more available in the rental market. Before it was adopted, it’s prohibited to have, for example, three or more people sharing an apartment unit. Now that’s been relaxed in some cities, allowing for more migrant workers to share one unit to keep the rates down for them. You see a little bit more affordable rental units available in the market now.

I just read Thomas Campanella’s The Concrete Dragon, and he talks a lot about the scale of displacement in the 1990s and 2000s. Massive urban renewal projects where over 300,000 people in Beijing lost homes to Olympics-related development. Or Shanghai and Beijing each losing more homes in the ‘90s than were lost in all of America's urban renewal projects combined. It didn't sound like those displaced people had much of a voice in the political process. But that book was published in 2008.  How has policy changed since then, especially if people are more willing to engage in activism?

First of all, I want to make a justification for urban renewal in Chinese cities, which were developed mostly in the ‘50s and ‘60s. At the time, [in the 1990s] the conditions weren’t good and allowing for better standards of construction would inevitably have to displace some of the residents in older settlements. In my personal opinion, that wasn't something that could be done in an alternative way.  

Still, in the earlier days, the way of displacing people was really arbitrary, that's true. There wasn't much feedback gathered from the public or even from the people affected. In the name of the public interest, in the name of expanding a road, or expanding an urban center, that's just directed from the top down. 

Nowadays things are changing. The State Council realized they needed more inclusive urban development, they needed to have all the stakeholders heard in the process. In terms of how to process urban development, and sometimes displacement, the way that they are dealing with it now is more delicate and more inclusive.

Can you give me an example of what that looks like?

For example, [consider] hutong in Beijing, the alleyway houses, a typical lower-density [neighbourhood] that needs to be redeveloped. In the past, a notification was sent to the neighbours: “You need to be replaced. You need to be displaced, we need to develop.” That's it. 

Nowadays, they inform all different sorts of stakeholders. They could include artists' associations, nonprofits, grassroots organisations that represent the interests of the local residents. Then they [the citizens groups] could say what they really want to preserve. “This is what we think is really valuable” and that will be part of the inputs in the planning process. Some of the key elements could possibly be preserved. They  [the authorities] also talk about the social network, because they realized that when they displace people, the biggest loss is the social network that they have built in the original location. So, it's not only conserving some of the physical environment, but also trying to conserve some of the social network that people have.  

(STR/AFP via Getty Images)

Speaking of urban renewal, there was a big emphasis in the ‘90s and 2000s on highways. A lot of auto-oriented development in Beijing, following more of a Los Angeles than New York model. There's this quote I saw from Hong Kong architect Tao Ho, during the 1990s development of Pudong in Shanghai, warning against replicating “the tall buildings and car-oriented mentality of the West." 

In the ’90s or the first decade of the 21st century, most cities in China were still making mistakes. When I was a student, in the late '90s, I was translating for the American Planning Association. At the time, Beijing was still taking out the bike lanes and the planners from APA were telling them: “No, don't do that. Don't make that mistake." 

In the past decade, that's not occurring anymore. It has been happening [adding bike lanes] for a couple of years in Beijing, Shanghai, Shenzhen. More attention has been given to improving the service quality of green transportation, upgrades to buses, the bike lane system, and so on. 

As China got richer, bikes became a symbol of poverty and, like you said, urban planners began removing bike lanes. Cities like Nanjing and Shanghai considered banning bikes from the central city entirely. 

For a long time, bike lanes were abandoned and the road surface was more devoted to the car. But in the past few years this has been changing, more road space has been given to bus rapid transit and to bike lanes. The attitude giving precedence to the private car is giving way.

Another thing they are trying to do is behavioural change, teaching younger generations that biking is cool, creating a new set of values that's more sustainable. In some major cities, you see educational campaigns, posters around the cities, [saying] bicycling is really cool. 

A recent paper you worked on looked at air quality in Chinese cities and found they are still struggling. The paper cited a study suggesting “that Chinese cities face the worst air quality across different cities around [the] world based on an extensive research of 175 countries.” Your paper recommends transit-oriented development and significant green outdoor space. Is that something you see policymakers adopting?

Yes, definitely, although with regional variations still. The eastern and southern cities are seeing more policies toward transit-oriented development. They are adapting smart technology too. For example, Hangzhou, which is the model of smart cities, the tech tycoon Alibaba installed sensors on every single traffic signal there. Then they were using technology to change the light, so when they detect a higher volume of traffic, they streamline the green lights and the red light wouldn't stop the cars, so there are less carbon emissions at the intersections. They showed that there was a reduction of up to 15% emissions. 

What about in terms of parking policy? How are policymakers trying to deal with the influx of cars in these cities? Are there parking minimums like in many American cities?

I was visiting Hangzhou in December, their “Smart City” headquarters there. They were trying to use technology to let people know where there's parking, so they don't have to drive around, which increases carbon emissions. In other cities, like Shenzhen, they were increasing the parking fee in the downtown by 50 yuan, or seven US dollars an hour. That's pretty high in the context of Chinese cities. It was 10 or 20 yuan before. So, just increasing the parking cost in the downtown area so that you discourage people from driving.

What are you working on now?

My new research is still on air quality. We had a really cool collaboration with a counterpart of Google Street Map. In China, that’s Baidu StreetMap. We asked the company to install another sensor on their cars when they take pictures. We added a sensor for air quality. So, we will know at a street level what are the current emissions by geolocation, by time. That will be really cool when we have all that data. 

Jake Blumgart is a staff writer for CityMetric.