How do you map a city with no centre? Commuting patterns in the San Francisco Bay area

The Golden Gate Bridge, San Francisco Bay. Image: Justin Sullivan/Getty.

Dr Alasdair Rae is a senior lecturer in the geography department of the University of Sheffield.

I’ve recently been writing and thinking about polycentric urban regions: partly because I’m interested in how places connect (or not) for one of my research projects, and partly because I’ve been experimenting with ways to map the connections between places in polycentric urban regions.

There was quite a lot of the latter in Peter Hall and Kathy Pain’s ‘The Polycentric Metropolis’ from 2006 – but given that the technology has moved on a little since then I thought I’d explore the topic in more detail. Mind you, I’ve also been looking back on Volumes 1 to 3 of the Chicago Area Transportation Study of 1959, as a reminder that technology hasn’t moved on as much as we think: their "Cartographatron" was capable of mapping over 10m commuting flows even then, although it was the size of a small house and required a team of technicians to operate it.

Anyway, to the point… What’s the best way of mapping polycentricity in an urban region? 

For this, I decided to look at the San Francisco Bay Area since it has been the subject of a few studies by one of my favourite scholars, Prof Robert Cervero of UC Berkeley. Also, a paper by Melanie Rapino and Alison Fields of the US Census Bureau identified the Bay Area as the region with the highest percentage of "mega commuting" in the United States – that is, people who travel 90 or more minutes and 50 or more miles to work. 

Therefore, I decided to look at commuting flows between census tracts in the 9 counties of the Bay Area, from Sonoma County in the north to Santa Clara County in the south. I’ve used a cut-off of 30 miles here instead of the more generous 50 mile cut-off used by Rapino and Fields. I also mapped the whole of the United States in this way, but that’s for another day.

Are you in the big blue blob?

The series of maps below illustrate both patterns of commuting in the Bay Area and the different approaches I’ve taken in an attempt to capture the essence of polycentrism in the area. I don’t attempt to capture the misery of some of these commutes (for that I’d need a different kind of technology).

But, I do think the animations in particular capture the polycentric nature of commuter flows. If you’re represented by one of the dots in the images below, thanks a lot for taking part!

Let’s start with a simple representation of commutes of over 30 miles from San Francisco County (which is coterminous with the City of San Francisco). The animated gif is shown below.

The most noticeable thing here is the big blue blob(©) making its way down from San Francisco to Palo Alto, Mountain View and Cupertino in Santa Clara County. In total, the blue dots represent just over 15,000 commuters going to 803 different destination census tracts.

I’m going to take a wild guess and suggest that some of these commutes are by people who work at Stanford, Google and Apple. But it probably also includes people working at NASA Ames Research Center, Santa Clara University and locations in San Jose. 

These patterns aren’t particularly surprising, since there has been a lot of press coverage about San Francisco’s bus wars and commutes of this kind. However, there is a fairly significant dispersal of San Francisco commuters north and east, even if the numbers don’t match those of the big blue blob. By the way, from San Francisco it's about 33 miles to Palo Alto, 39 miles to Mountain View, 42 to Cupertino and 48 to San Jose. 

The first example above doesn’t reveal anything like the whole story, though. There are actually quite a lot of commuters who travel in the opposite direction from Santa Clara County to San Francisco. And more widely, the commuting patterns in the Bay Area – a metro area of around 7.5 m people – resembles a nexus of mega-commuting.

This is what I’ve attempted to show below, for all tract-to-tract connections of 10 people or more, and no distance cut-off. The point is not to attempt to display all individual lines, though you can see some. I’m attempting to convey the general nature of connectivity (with the lines) and the intensity of commuting in some areas (the orange and yellow glowing areas). 

 

Even when you look at tract-to-tract connections of 50 or more, the nexus looks similar.

 

If we zoom in on a particular location, using a kind of "spider diagram" of commuting interactions, we can see the relationships between one commuter destination and its range of origins. In the example below I’ve taken the census tract where the Googleplex is located, and looked at all Bay Area Commutes which terminate there, regardless of distance.

In the language of the seminal Chicago Area Transportation Study I mentioned above, these are "desire lines" since this represents "the shortest line between origin and destination, and expresses the way a person would like to go, if such a way were available" (CATS, 1959, p. 39) instead of, for example, sitting in traffic on US Route 101 for 90 minutes.

According to the data, this example includes just over 23,000 commuters from 585 different locations across the Bay Area. I've also done an animated line version and a point version, just for comparison.

Commuting connections for the Googleplex census tract.

 

Animated spider diagram of flows to Mountain View.

 

Just some googlers going to work, probably. 

Looking further afield now, to different parts of the Bay Area, I also produced animated dot maps of commutes of 30 miles or more for the other three most populous counties – Alameda, Contra Costa and Santa Clara. I think these examples do a good job of demonstrating the polycentric nature of commuting in this area, since the points disperse far and wide to multiple centres.

Note that I decided to make the dots return to their point of origin – after a slight delay – in order to highlight the fact that commuting is a two way process. The Alameda County animation represents over 12,000 commuters, going to 751 destinations, Contra Costa 25,000 and 1,351, and Santa Clara nearly 28,000 commuters and 1,561 destinations. The totals for within the Bay Area are about 3.3m and 110,000 origin-destination links.

Alameda County commutes of 30+ miles.

 

Contra Costa County commutes of 30+ miles.

 

Santa Clara County commutes of 30+ miles.

 

Finally, I’ve attempted something which is a bit much for one map, but here it is anyway; an animated dot map of all tract-to-tract flows of 30 or more miles in the Bay Area, with dots coloured by the county of origin. Although this gets pretty crazy half way through I think the mixing of the colours does actually tell its own story of polycentric urbanism. For this final animation I’ve added a little audio into the video file as well, just for fun.

A still from the final animation. You can see the whole thing here.

What am I trying to convey with the final animation? Like I said, it's too much for a single map animation but it's kind of a metaphor for the messy chaos of Bay Area commuting (yes, let's go with that). You can make more sense of it if you watch it over a few times and use the controls to pause it. It starts well and ends well, but the bits in the middle are pretty ugly – just like the Bay Area commute, like I said.


My attempts to understand the functional nature of polycentric urbanism continue, and I attempt to borrow from pioneers like Waldo Tobler and the authors of the Chicago Area Transportation Study. This is just a little map-based experimentation in an attempt to bring the polycentric metropolis to life, for a region plagued by gruesome commutes.

It’s little wonder, therefore, that a recent poll suggested Bay Area commuters were in favour of improving public transit. If you're interested in understanding more about the Bay Area's housing and transit problems, I suggest watching this Google Talk from Egon Terplan (54:44).

Dr Alasdair Rae is a senior lecturer in the geography department of the University of Sheffield. 

This article was originally posted on his blog, Under the Raedar, and is reposted here with the author's permission.

 

NOTES: The data I used for this are the 2006-2010 5-year ACS tract-to-tract commuting file, published in 2013. Patterns may have changed a little since then, but I suspect they are very similar today, possibly with more congestion.

There are severe data warnings associated with individual tract-to-tract flows from the ACS data but at the aggregate level they provide a good overview of local connectivity. I used QGIS to map the flows. I actually mapped the entire United States this way, but that’s going into an academic journal (I hope).

I used Michael Minn’s MMQGIS extension in QGIS to produce the animation frames and then I patched them together in GIMP (gifs) and Camtasia (for the mp4s), with IrfanView doing a little bit as well (batch renaming for reversing file order). Not quite a 100% open source workflow but that’s because I just had Camtasia handy. The images are low res and only really good for screen. If you’re looking for higher resolution images, get in touch. 

 
 
 
 

American policing never adjusted to the decades-long decline in urban violence

Joe Raedle/Getty Images

Princeton University’s Patrick Sharkey is an almost impossibly prolific academic, regularly publishing an array of well-regarded studies on everything from social distancing to neighbourhood change. But in recent years he’s become best known for his work on criminal justice and law enforcement – topics that have risen to the top of America’s policy agenda.  

Sharkey’s last book, Uneasy Peace, is about the dramatic decline in crime rates in American cities, what caused it, and what is needed to sustain it. Published in the wake of the Black Lives Matter movement’s emergence in 2014, it deftly analyzes issues that are again roiling America after the killing of George Floyd. 

Uneasy Peace, and the work Sharkey has published since Floyd’s murder, argues for a massive campaign to address violence in American cities. But that does not mean flooding the streets with more police officers. CityMetric spoke with Sharkey about the little-known factors behind America’s great crime decline, the need for massive public investment, and what community policing looks like without the police.

Why did violent crime in the US, and in American cities particularly, fall so sharply between the early 1990s and the early 2010s? 

Violence from the late 1960s through the early 1990s was at an extreme level. There was a crisis of violence throughout much of urban America, particularly in the big cities. Then something happened in the 1990s. It happened because both political parties took on crime and violence as central issues in their platforms. Bill Clinton ran on a platform that he was tougher on crime than the Republicans had been. The whole country saw violence as a national crisis.


What happened in the early 1990s is there was a large-scale mobilisation to retake public spaces and make cities safe. That consisted of several parts. There was a really large-scale effort to bolster police forces, to invest in more aggressive tactics of policing, to go after gang activity, to shut down drug markets.

At the same time there was a large-scale expansion of local organisations that really mobilised to make their communities safer: after-school programs, religious organizations, community centres, neighbourhood groups. These kinds of organisations expanded in a major way.

What I find is that the expansion of those kinds of community organisations stands alongside the expansion of police forces as components of why violence fell. They combined with expansion of video surveillance, camera systems, and private security. All these things happened at roughly the same time, and public spaces transformed. That's why violence fell so dramatically, beginning in the early 1990s.

The crime decline benefited everybody, making urban areas safer, and convincing more middle- and upper-income people to move back to cities. But you argue that those who live in the most violent neighbourhoods benefited the most, because violent crime declined most in those areas. What has changed in these communities as they've seen less crime?

The most obvious benefit is that tens of thousands of lives were saved, with the greatest impacts experienced by Black men. We found that for most groups, life expectancy wouldn't change that much if homicide never fell. But for Black men, there was an enormous change: the life expectancy of Black men rose by almost a year due purely to the drop in homicide mortality. That is a change as large as any public health advancement over the past several decades.

Then there are direct consequences for academic achievement. The places where violence dropped the most are places where statewide test scores rose the most. And children who were in places that became less violent over the course of their childhood were much more likely to rise up in the income distribution in adulthood and to make more income as adults.

Violence has a long reach. There's a direct effect of violence on every institution, every member, every child within that community. It damages kids’ cognitive development and academic functioning. So, when violence falls, kids are able to learn, kids are able to focus in school if they're not thinking about the threat of violence.

Then it has an indirect impact because life returns when a community becomes safer. Businesses start to set up shop, families invest in that neighbourhood, it becomes a vibrant place again, and that means more jobs are there, that means more opportunities are nearby. That changes the possibilities for a child as they near adulthood and enter the labour market. All this translates into improved economic outcomes later in adulthood.

You point to research that shows aggressive policing and imprisonment has been part of the story of America's great crime decline, but at immense human cost. You note that while every other kind of violence has fallen since the early 1990s, the rates of police violence remain consistent.

Why hasn't police violence responded to what's happened everywhere else?

We invested heavily in an aggressive style of policing. We asked police departments to go take over city streets and reduce violence by any means necessary. That was a conscious policy decision made in the 1980s and 1990s. It was supported by most Americans. Not everyone, but it had support across the political spectrum. It had support from Black and white Americans. Not universal support, but it did have strong support. 

What has changed over time is that as violence fell, as city streets became safer, the strategies that police departments use didn’t change.

I lay out two policy questions toward the end of the book. The first is how can we make sure that violence keeps falling? The second one is how can we do it with a new approach that doesn't rely on the prison system and the aggressive policing of the past few decades. That's the challenge right now: What's the next model?

What do you make of calls to defund or even abolish the police? In your book, you say that every video of police brutality makes it harder to reimagine a new role for the police. Did the George Floyd video make it impossible?

It might be impossible. There are lots of neighbourhoods where the institution has lost all credibility, and that happened a long time ago. More people are coming to that conclusion now.

We need a new model to deal with the challenge of violence. If we pursue a policy agenda that is designed to simply exact revenge against the police and try to destroy this institution, we're going to leave cities vulnerable. If we pursue an agenda that just attempts to dismantle the police before an alternative institution is ready to take responsibility, then we run the risk of destabilising neighbourhoods. That's my biggest concern.

Over a longer term, I think the role of the police should be dramatically reduced. We have great evidence that local community organisations, in combination with residents, are at least as if not more effective at controlling violence. They've just never been given the same resources, the same commitment.  


(Justin Sullivan/Getty Images)

At the end of your book, you call for a “war against violence.” To fight that war, investment is needed if these groups are going to take the place of the police. But we seem to be embarking upon a new age of austerity. What could the ramifications for urban violence be if the US Congress fails to support city and state governments?

Austerity is not inevitable, but it doesn't look like this Congress is preparing to invest in state and local governments. It's not inevitable that we're going to see a period of fiscal crisis in cities. That's a policy choice but if that happens, if city budgets are reduced and funding for local community organizations drops, we'll probably see a rise in violence.

When cities and communities are abandoned, that's what happens. That's why violence rose the first time. In the early 1970s, the federal government abandoned its support of central cities, the power structure of state governments shifted toward suburbs. If funding for cities and local organisations falls, we should expect a rise in violence. 

You write about a newer institution in Australia’s Aboriginal communities that patrols the streets, unarmed, to defuse situations and address issues – everything from domestic disputes to public drunkenness – in place of the police.  But the role of this community patrol, and neighbourhood groups in the US, is about prevention. Is there a role for law enforcement in ensuring that those who commit murder and violence are punished?

Yes. I think the model that we need to work toward is one where a different set of actors are responsible for overseeing public spaces and making sure everybody is safe, everyone is supported within those communities. Then the police play a secondary role.

That means when there's a mental health crisis, you have trained mobile response teams who are the first to respond to those incidents. Patrol of a neighbourhood should not be carried out by police officers, it should be carried out by advocates, by neighbours who are well trained and genuinely concerned for the well-being of their neighbours. At the same time, I argue that there is a role for police. In places where gun violence is extreme, it's potentially harmful to relieve the police of all responsibilities. There are weapons crimes where I think the police should still be the first to respond. There is a role for police because gun violence is so extreme in the US.

The biggest change, which is not often mentioned in these discussions, is in patrol. The people who are out in public space, making sure that no problems emerge, making sure that kids are safe, that they're getting where they need to go. Making sure that if someone comes home from the late shift, they have someone they can see in public space and know that they're okay, know that they'll be safe walking home.

That should not be police officers. There are too many communities where the level of mistrust is too severe. It should be other members of the community who are trained professionals, whose job is to be a pro-social presence in public space. That's one major change that I don't think is mentioned enough in these debates about who should do what. Who should be a pro-social presence in public space?

You cite research that suggests that despite the crime spike between the late 1960s and the early 1990s, the second half of the 20th century was less violent than the first half. So despite recent crime spikes in some cities, and what appears to be a surge in domestic violence related murders during the pandemic, does that mean we are living in one of the most peaceful periods in American history?

Yeah, without a doubt. The data before 1950 are not great. But the best evidence we have suggests that violence has been falling over the history of our country. There have been periods with more and less violence, but without a doubt, we are living in one of the safest periods in US history.

We need to focus a great deal of attention on violence. It is the fundamental challenge of cities. But along with urgency, we have to be aware of progress that's happened over time. New York is going to have a higher level of violence this year, in all likelihood, than it had a couple of years ago. That's something we need to maintain focus on. New Yorkers are dying.

But we also have to remember that there were 2,200 murders [annually] in New York in the early 1990s. There will be somewhere between 300 and 400 this year. That’s urgent, but let's also celebrate progress and make sure we have an accurate perception of the level of violence and that we don't exaggerate short-term fluctuations.

Jake Blumgart is a staff writer at CityMetric.