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.