 City-building is the great challenge of the 21st century. And it is just amazing to be surrounded by such smart, creative, passionate people who recognize that. And who recognize that as difficult as city-building is, it has enormous potential. It has potential for health, for prosperity, for democracy, for creativity, for beauty. And that is why we are here, and that is why the urban age is such a wonderful, wonderful thing. I want to start with an old piece of infrastructure, the aqueduct, right? And I want to start with it for two reasons, one of which is the narrow technical point, which is that there is no more important job for city government than clean water. There is no crime wave that is as deadly as a cholera epidemic. And bringing in clean water and bringing out sewage is absolutely central to making our cities habitable, safe, and healthy. The second reason I want this aqueduct, though, is it reminds us that infrastructure can also be beautiful. And that is in some sense the parallel challenge, that we need to both figure out ways to make our cities safe, but also to make them places of joy, make them sing, to build things that we hope in 2,000 years people will still be looking at them and say, this is magic. And of course, you know, all of this magic depended critically on infrastructure, because in fact the cities would have perished if disease had stalked through them if they hadn't had clean water. So as boring and as tough as infrastructure can often be, everything depends on it. And that's really the point of my talk here. Now, we've seen a lot of triangles, almost all of them with more aesthetic sense than I will show, because of course I'm an economist and that by definition means that I lack aesthetic sense. But my triangle is this, that when I think of cities, I think of a triad. I think of cities at their core starting with the magical human interactions that happen when people are close to one another. This is markets. This is the spread of ideas in Renaissance Florence. This is the learning of knowledge that John Snow did in London in 1854. This is the passing of trade. This is the whole possibilities that human beings have, because of course cities make us more human. Our greatest talent as a species is our ability to learn from one another, our ability to work together, and cities have been making that happen for thousands of years. Now, in addition to that magic is a darker side, for there are demons that also come with density. If two people are close enough to exchange an idea face to face, they're also close enough to exchange a contagious disease. And if someone's close enough to sell you a newspaper, they're close enough to rob you. And that is why we have to need a robust public sector to manage the demons that come with density. To manage crime, contagious disease, traffic congestion, sometimes high housing costs get thrown in there. And then there's the third aspect of the city, the physical city, the structures, the infrastructure that exists to serve the people, but also to create the lasting imprint of the city, to direct its path. And infrastructure is very much the marriage of that physical city and the process of battling the demons that come with density. Now, you've also seen, again, from people with far more aesthetic sense than me, maps that show the changing urbanization of the world. Now, this is how an economist maps it, not with geography but with income. So what I've done is I've taken all of the poorer countries in the world and I've sorted them on the basis of their per capita income. So each one of those bars are 4,000 to 5,000, 3,000 to 4,000, and you're looking at both 1960, which is the blue bars, and 2010, which is the red bars. I've, of course, corrected for inflation between 1960 and 2010. And the height of the bar shows the share of cities in each income bracket that is more than one-third urban. One-third urban is a relatively arbitrary number, but it gives you a sense as to whether or not this plays as cities. So in 1960, 80% have cotton trees with incomes between $4,000 and $5,000 were more than one-third urban. About the same number is true today. In 1960, an even larger share with incomes between $3,000 and $4,000 were more than one-third urban that are today. But again, a very high quantity. But go down and look at the poorest cities, poorest countries. What share of those countries with income levels less than $1,000 were more than one-third urban in 1960? It's a really easy number to remember. It's zero. Because in 1960, which had been true throughout almost all of recorded history, to be poor was to be rural. Today, you can see more than 40% of such highly poor countries are more than one-third urban. Now, if you go to 1,000 to 2,000, the shift is between one in five such countries are more than one-third urban to almost 60%. Now, Latin America led the way. Latin America came first with having urbanization before well. But now we see this in sub-Saharan Africa, in India. And in some sense, that is the background for all of the challenges that we're talking about. Because we are seeing places grappling with the downsides of urbanization with very limited financial resources and often very limited public capacity. And the great challenge of the 21st century is to make the cities in these places more livable, places of opportunity for all. Now, Jean-Claude made this point, which is, I think, central, which is that urbanization is development. And there are many ways of showing you this. I could mention the fact that when you compare those countries that are more than 50% urban to those countries that are less than 50% urban, the more urbanized countries have incomes that are on average five times higher. But I think it's even more important to look at growth. So here you're looking at urbanization in 1960 and growth between 1960 and 2010. It's not a perfect relationship, but boy, it's enormously strong. The places that moved into cities experienced faster income growth. I know of no pathway out of poverty into prosperity that does not run through city streets. And even more importantly, cities have bet the process of democratization. They have bet cultural leaps. They have bet a process of freedom, right? There's an old German proverb that city air makes you free, and that continues to be true today as it was in medieval Germany. This link between cities and developed cities and wealth means that the process of dealing with sewers in Manila is on the front edge of the human experience, the process of building and informal settlements in India, the process of dealing with crime in Latin America. This is the stuff of which humanity's future is made. And we should remember, as challenging as it is, that it also should be joyful, that cities are places of fun and pleasure as well as challenge. And by working on city building, you are doing something that can materially change and better the lives of millions. Now, I want to start with... I want to move now to Deravi, right, which is a place that epitomizes in some sense the challenge ahead. Here we have a place that is full of enormous energy, right? Incredible entrepreneurship that India just bubbles with. And, you know, pride in products that are being made, small-scale entrepreneurship, the flow of information that makes cities great, and yet, you know, you walk outside and you see a kid defecating in an unpaved road. And it reminds you of the incredible need for public investments in the cities of the developing world. Another way of looking at this, this is the relationship between income and share of deaths due to communicable diseases across the world, right? This is what happens when infrastructure fails. People die. And that is why it is so important to be ruthlessly pragmatic when thinking about this infrastructure. And I'll return to that in a second, but it is an incredible mistake to think that just privatizing infrastructure is the answer. It never is. But on the other hand, it is also a mistake to think that just putting it into the public sector is an answer as well. That, in fact, appropriate institutional design is hard and critical because otherwise people die. This is a path rate of death rates in New York City over the past 200 years. And in fact, New York tells the story of an attempt to create a private water company to handle the death rates of the 1790s that failed miserably. The company, the private company that was meant to do it is still around, its name is J.P. Morgan Chase, which was the Chase Manhattan Bank, which was the Bank of the Manhattan Water Company, and it's always done a lot of banking and never done much in terms of water. You didn't have changes until you had a public system, until you had the Croton Aqueduct and indeed, America's cities and towns were spending as much on clean water at the start of the 20th century as the federal government was spending on everything, except for the post office and the army. Investments are necessary, but more than just engineering is necessary because I want you to look at this thing for a second, look at this figure. The Croton Aqueduct, the great piece of infrastructure, I'll show you the picture here. This is the great Croton Aqueduct. It's built in 1842. For 25 years after this, we have cholera epidemics. For 25 years, people are dying. Why? Why is it that engineering wasn't enough? Well, it's the same problem we see in Sub-Saharan Africa today, which is the last mile problem. Poor people weren't willing to pay for the connection fee. They continued to use wells, shallow wells, they continued to use pit latrines, and they continued to die. Yes, there was some attempt to subsidize, but that attempt to subsidize wasn't enough. They put an open hydrant, one for every 10 blocks or so, too far away to carry water. A great grandfather died in that one of cholera in 1849. You needed to have policies that pushed people to use the new infrastructure. You needed to have rules that said that landlords had to connect to the sewers. It's not just enough to build the engineering. You actually have to change behavior around it. And indeed, as we think about this problem in the developing countries of the world, there are two things to think about when we think about changing behavior. One of which is we don't trust the existing cops too often, because we need to have parallel processes that can nudge people towards putting in sewers, towards dealing with septic tank problems that don't involve relying on trustworthy police. And secondly, we need to deal with the fact that we don't know who owns the land, because part of at least the New York process meant at least you knew who owned the land, so you could actually ask them to make these requirements. This is very much what we're dealing with in my own work in water in Lusaka today, right? The proximity of the wells and the latrines. And one way to think about water is there are multiple technologies for delivering it. Right? In some cases, it's okay to upgrade the existing technologies to move to septic. In some cases, when density gets higher, you need wholesale moves to collective more expensive technology. Another case in which infrastructure is not enough is highways. There's something the economist, Gilles Gerainton and Matthew Turner have called the Fundamental Law of Highway Traffic. Vehicle miles traveled increased roughly one-for-one with highway miles built. If you build it, they will drive it. Okay? You need to change behavior, and you change behavior by putting in prices. Singapore has had electronic road pricing for the past 30 years, and the streets moved swiftly during all times of day, because people paid for the social costs of their action for the pollution and congestion that they create. Buses. Bus rapid transit. This is Bogota, right? A pioneer on this. There's a lot to be said for buses. In part, their flexibility. They can be moved around. In part, their low costs. And they can be environmentally friendly as well. Right? Buses are a fantastic technology. Two final points. One of which is when you think about the built environment, there is a Silla and Charybdis out there. There are Silla and Charybdis. One is Nimbism. It's epitomized by Mumbai here. Saying no to everything. You can't say no. You have to build, and you have to make the building process feasible and humane and sensible, right? On the other hand, the second demon is monumentalism. Forgetting that the real city is the humanity, and thinking that the real city is the structures. And you build for the sake of looking at shiny towers, and there's Astana there, rather than building for the actual human needs. And the last point I want to make is just one of the reasons why we build, and why the reasons why we like density, is that in fact, what looks green is often brown, and what looks brown is often green. And this is some work with Matthew Kahn on measuring carbon emissions in different parts of the US. Because when you, looking at people of comparable income and family size, compact living means smaller apartments, which means less energy use, and means less driving. And for that reason, we all have a lot to gain if the great growing economies of India and China see themselves grow up rather than out. If their per capita emissions rise to those seen in the sprawling United States, global carbon emissions go up by 130%. If they stop at the level seen in wealthy but hyper-dense Hong Kong, global carbon emissions go up by less than 30%. We all have a lot to gain from compactness, but even more so, we all have a lot to gain from the magic that comes when people learn from each other in cities. Thank you. It's very easy to see why you've been one of the people who's been at the cutting edge of making the case for cities. And that's been really important as we've advanced. But I was struck when you were talking that it's a very modernist understanding of the city. It's a very masculine, perhaps, understanding of the city. But it's an idea where, these are phrases you used. Urbanization is development. We can manage the demons. We can harness growth ruthlessly. Pragmatic thinking about infrastructure is possible. And I suppose what I'm wondering about is, is it possible to conceive of the city and of urbanity in terms which acknowledge or embrace the idea that you might have the persistence of traditional values, the perpetuation of gender discrimination, the rejection of a growth agenda? Is that not possible in your vision of the city? I wonder if you could just talk to us about whether you've got a kind of rather linear growth-oriented aspirational agenda. It's a great question. I think there's a reason why part of the glory of the urban age is that we have multiple disciplines. Because in fact, unquestionably, the perspective of an economist tends to be slightly different than other perspectives. That being said, I think almost everything that you mentioned, I actually believe in, I believe that cities can accommodate. So it is, great cities do not cut themselves off from the lands where their people came from or from the cultures that they came from. Great cities manage to enable space for those cultures and watch them change and watch them become special and unique. And certainly, if we think about the glory of the New York City of my youth, a lot of it was that the sending countries weren't lost, that they were still there. The growth agenda, yeah, I kind of do think that more wealth is better than less in the same sense that I think that more health is better than less and that not more happiness is better than less, but it certainly isn't the only thing that matters. And I think the right thing is we balance different things and we make sure that growth doesn't occur at the expense of the other things that are magical. But I don't think there's any future in rural poverty either. So we're talking, it's not just that those more urbanized countries have incomes that are five times higher, they have infant mortality levels that are less than a third. And I'm always rooting against the death of children.