Hello and welcome to Unit 7

The topic of this unit is scaling in urban systems.

This will be the last unit, the last full unit in the course.

And it’s a little bit shorter than usual.

The reason for this is that the topics

I’ll be discussing are still very much

areas of current and ongoing research.

So there is not a final neat story that I can tell.

Instead I’ll try to give a snapshot of some results

and give my best sense of where things are now

and there are a bunch of papers and talks

that you can dig into to learn more

So the central idea, the central questions behind

urban scaling are similar to those of metabolic scaling.

So for metabolic scaling we asked

how does a system metabolism change with its body mass.

And we saw that that system to a very good approximation

exhibit scaling that the relationship is described

by a power law with a 3 quarters exponent.

And than there is a nice mechanistic theory to explain

why that power 3 quarters appears.

So urban scaling starts with some similar questions.

How do properties of a city vary

as the population of the city changes,

If I double the size of the city

what would I expect what happened to its GDP

or the number of patents files per capita by city residents

or the total number of traffic lights or gas stations

or the total length of roads.

So empirically, one sees at the data is

more or less described by a power law.

We’ll see that the fits certainly are

as clean as for metabolic system.

But there is some reason that

we wouldn’t expect them to be as well.

So I’ll present first some empirical results suggesting

or providing evidence that scaling occurs in cities

and we’ll talk about may be what’s interesting about that

and what that might mean.

And then I’ll say a little bit about some ideas

for possible mechanisms or explanations for these power laws

or power law like behavior that we see.

So let’s get started by looking at some of the empirical evidence

suggesting that there may be scaling in urban systems.