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 can cities become more bike friendly? The Netherlands offers useful lessons

(Aurore Belot/AFP via Getty Images)

It might seem like cycling is in the DNA of the Netherlands, a country where even the prime minister takes his bicycle to work. But the Dutch haven’t always lived as one with their bikes. In the Amsterdam of the early 1970s, cars were considered the wave of the future. They can be seen filling up squares and streets in historical photographs, and killed an average of over two Amsterdammers per week, including many children.

It is nothing more than an “accident of history” that the Netherlands embraced cycling, says Marco te Brömmelstoet, the director of the Urban Cycling Institute in Amsterdam and a man better known as the city’s cycling professor. Today’s bike rider’s paradise was created after parents and activists took to the streets to protest “child murder” by car. A Saudi oil embargo, rising gas prices, concerns about pollution and anger about the destruction of entire neighbourhoods to build motorways did the rest. 

Amsterdam, 1958. Not a cyclist's paradise. (Keystone/Getty Images)

What’s important about this history is that it can be replicated in other cities, too. Of course, the Netherlands has certain advantages – it’s flat as a pancake, for example. But in the eyes of traffic reformers, the rise of e-bikes (and even cargo bikes) means there’s no excuse for prioritising cars everywhere. 

So how can cities, flat or not, follow Amsterdam’s path to creating places where cycling is a pleasant, safe and common way to get around? The Dutch have some tips. 

Separate bikes from car traffic

Any city could start painting dedicated bike lanes on the streets. But in the Netherlands, those white marks indicating space for cyclists are considered just a minor first step. 

“A line on the road is not enough. Motorists will ignore it,” says Frans Jan van Rossem, a civil servant specialising in cycling policy in Utrecht. If other cities want their residents to choose bikes instead of cars when dodging pandemic-era public transport, protecting them from fast-moving car traffic must be the priority, Van Rossem says. 

The Dutch research institute CROW developed a widely praised design manual for bicycle infrastructure, full of tips for creating these protected lanes: A row of vertical white posts or a curb can serve as a physical separator, for example. Still, cyclists tend to feel safest in a "solitary" path, separated from the road by grass, trees, or an elevated concrete island. 

“The main bottleneck, the main reason why people don’t cycle, is that they don’t feel safe,” Van Rossem notes. “To start, construct separate paths.”

Turn those bike paths into a network

Many cities may have some bike lanes on some streets, but leave cyclists to roll the dice everywhere else. Will conditions still be safe when they turn left or right? Often they have to continue their way without any protected facilities for cyclists. 

“In many cases, cities take fast action, without thinking it through very well,” says Lucas Harms. He leads the Dutch Cycling Embassy, a partnership between the Dutch government and several companies, which promotes Dutch bike knowhow globally. “Don’t build small pieces of bike lane from nothing to nowhere. Think about a network of cycling infrastructure.” 

Utrecht aims to have cyclists within 200 to 300 metres of a connected path anywhere in the city, Van Rossem says. Avoid constructing those paths in sketchy industrial areas, he warns. “A connection through an unattractive area may be fast, but won’t be used a lot.”

Embrace the ‘fietsstraat’, a street where bikes come first

On some streets, drivers have to give up their privileges. (Rick Nederstigt/AFP via Getty Images)

A peculiar Dutch invention called "fietsstraat" (cycling street) holds strong potential for the rest of the world, Kevin Krizek says. He’s a transportation professor from Colorado who spent three years at Radboud University in Nijmegen. 

On cycling streets, cars are “guests”, restricted by a speed limit of 30 kilometres per hour. Drivers are not allowed to pass, so cyclists comfortably dominate the road. In the Netherlands the fietsstraat is usually paved with red asphalt, to resemble a bike path and notify drivers of their secondary status. But creating a cycling street can be easy. “All you need to do is put signs at intersections,” Krizek says. The effect is revolutionary in his view. Drivers have to give up their privileges, and cyclists can take the lead. 

Some Dutch traffic experts worry the cycling street won’t work if a city doesn’t also have a robust cycling culture. In the Netherlands, drivers are aware of the perils of urban cycling because they too use bicycles. Moreover, Dutch cities use sophisticated “circulation plans” to direct cars away from city centres and residential areas, onto a few main routes. 

Without “calming” traffic this way, the cycling street could be a step too far, Harms says. “In a city like New York, where all roads are equally accessible and full, it’s better to separate bicycles and cars,” he says.

Redesign intersections for cyclists' safety

If cyclists have to cross intersections “at the mercy of the Gods”, you’re not there yet, says Harms. When he travels abroad, he often finds clumsily designed crossings. As soon as cars turn, cyclists may fear for their lives. 

Harms recommends placing physical barriers between cars and bikes in places where they must cross. The Dutch build elevated islands to direct traffic into separate sections. The golden rule: cars wait behind bicycles. That way, drivers can see cyclists clearly at all times. Barriers also force Dutch cyclists to turn left in the safest way possible. They cross the street first and wait for their turn again before making their way left.

“You can create that with simple temporary measures,” Harms says. Planters work fine, for example. “They must be forgiving, though. When someone makes a mistake, you don’t want them to get seriously injured by a flower box’s sharp edge.”

Professor Krizek points out how the Dutch integrated cycling routes into roundabouts. Some are small; some are big and glorious, like the Hovenring between Eindhoven and Veldhoven, where cyclists take a futuristic-looking roundabout lifted above the highway. Most of those traffic circles move high volumes of cars and cyclists through intersections efficiently and safely. For a simpler solution, the Dutch manual suggests guiding cyclists to quieter streets – crossing a block up or down may be safer. “Nobody knows how to do intersections better than the Dutch,” says Krizek. 

Ban cars, or at least discourage them

A man rides down from a three-level bicycle parking garage near Amsterdam's main train station. (Timothy Clary/AFP via Getty Images)

The quickest, most affordable way to make a city more bikeable is to ban cars, says Ria Hilhorst, cycling policy advisor for the City of Amsterdam. It will make streets remarkably safe – and will most likely enrage a significant amount of people. 

Amsterdam doesn’t outlaw cars, but it does deliberately make their owners feel unwelcome in the historic city’s cramped streets. Paid parking is hugely effective, for example. Many car owners decide to avoid paying and use bicycles or public transportation for trips into the city. Utrecht, meanwhile, boasts the world’s largest bicycle parking garage, which provides a dizzying 12,500 parking spots.

To further discourage drivers from entering the city’s heart, Amsterdam will soon remove more than 10,000 car-parking spaces. Strategically placed barriers already make it impossible to cross Amsterdam efficiently by car. “In Amsterdam, it is faster to cross the city on a bike than by car,” Harms says. “That is the result of very conscious policy decisions.”

Communicate the benefits clearly

Shopkeepers always fear they will lose clients when their businesses won’t be directly accessible by car, but that’s a myth, says Harms. “A lot of research concludes that better access for pedestrians and cyclists, making a street more attractive, is an economic boost.”

Try replacing one parking space with a small park, he recommends, and residents will see how it improves their community. Home values will eventually rise in calmer, bike-friendlier neighbourhoods without through traffic, Van Rossem says. Fewer cars mean more room for green spaces, for example.

“I often miss the notion that cycling and walking can contribute a lot to the city. One of the greatest threats to public health is lack of exercise. A more walkable and bikeable city can be part of the solution,” says Ria Hilhorst. “But in many countries, cycling is seen as something for losers. I made it, so I have a car and I’m going to use it, is the idea. 

“Changing this requires political courage. Keep your back straight, and present a vision. What do you gain? Tranquility, fewer emissions, health benefits, traffic safety, less space occupied by vehicles.” 

Again, she points to Amsterdam’s history. “It is possible; we were a car city too.”

Karlijn van Houwelingen is a journalist based in New York City.