One of the reasons I’m so fascinated by cities is that it’s becoming increasingly more important to get them right. From about 1831 to 1925, London was the largest city in the world. Its population went from somewhere around 1.5 to 2 million people to nearly 7.5 million. London surpassed Beijing as the largest city and was then surpassed by New York.

Today our largest cities are significantly bigger. Tokyo has almost 40 million people and London doesn’t even make the top 10. But there’s also a broader shift taking place. According to a new report by the United Nations, most of the world’s largest cities will be in Africa and Asia by 2030. Here’s a chart from Quartz:

And the reason for this shift is because Asia and Africa are newly urbanizing, whereas the rest of the world has already urbanized. In North America, over 80% of people already live in cities.

But even though Asia and Africa are following a trend that has already taken place in the rest of the world, it doesn’t mean we should assume we know what we’re doing. Having spent time in cities like Dhaka, I can attest to the many challenges that these mega-cities are facing and will continue to face as people flood in from the rural areas looking for economic opportunities.

So while it’s important that we talk about strategies for reviving cities like Detroit – which has a population somewhere around 700,000 - 800,000 people – we should also keep in mind that we have some significant challenges ahead of us in terms of creating a sustainable urban planning agenda for the world.

The tech community has been receiving a lot of backslash in San Francisco as of late. And Peter Shih’s infamous 10 things I hate about San Francisco post certainly didn’t help. But I think there’s a bigger issue than just rich tech people driving up the price of real estate.

I was reading Quartz this morning and I think they nailed it: 

"But the blame shouldn’t go to the tech companies or their employees moving to San Francisco, however despicable some might be. Blame San Francisco for being pleasant, and its policymakers for being foolish: When a lot of people are moving to your city—San Francisco the city gained 50,000 new residents between 2000 and 2012, including some 25,000 between 2010-2012 and likely more since—home prices are going to increase unless you build a lot more housing."

I’ve talked about this idea before. But I wanted to break it down a bit more precisely.

If San Francisco, the city, gained 25,000 people between 2010-2012, let’s say that the city gained roughly 8,300 people per year. I just divided by 3. However, if you look at the rate of new housing supply, you get a 10-year average of 2,350 housing units a year (from the Quartz article) and an even lower amount according to Atlantic Cities.

Regardless, what you end up with is a pretty simple phenomenon: More people are moving to the city than new housing is being provided and that’s driving up the price of real estate. In fact, San Francisco allegedly only created 269 housing units in 2011! That’s the equivalent of only one fairly typical Toronto condo building going up (and we have hundreds under construction). No wonder there’s upward pressure on prices.

So rather than just blame the tech community for the city’s housing problems, I think there needs to be a broader look at housing policy. If you really want to help affordability, here’s one simple solution: start building.