Your browser doesn't support the features required by impress.js, so you are presented with a simplified version of this presentation.

For the best experience please use the latest Chrome, Safari or Firefox browser.

The CityChrone project
accessibility studies in urban systems

Indaco Biazzo
Politecnico di Torino
SmartData@PoliTO - DISAT
personal page --
citychrone --

Distance between Society and Science

Generic placeholder image

Overspecialization in Science

Very difficult to cross the branches of science.

Slow learning curve

Very difficult to perform self-education path

Why it is a problem?

Make it difficults the creations of big communities working on the same projects

  • ~31M developers
  • ~96M repository
  • ~20k contributors (largest repository)
wikipedia [english]:
  • ~450K editors monthly
  • ~5M edits monthly
  • ~200k new pages monthly
  • ~1M contributors
  • ~2M points added per day
  • ~200k new ways added per day

And Games? People play avery days often to a very complicated games

crosswords, sudoku etc.
chess, go, domino
SimCity, fortnite, Minecraft etc..
Citizen Science
SETI@home [1999]: analyze radio signals, searching for signs of extraterrestrial intelligence . People can partecipate using their PC, donating their computational resources.

foldit [2008]: fold the structures of selected proteins as perfectly as possible, using tools provided in the game. Nature paper with credits more than 57000 authors.

Quantum Moves [2012]: simulations of logical operations in a quantum computer. Played over 8 million times by more than 200,000 players worldwide. The 200 000 players were all beaten by the stochastic optimization method. :(
Motivation 3

I was born in Rome

I had a very difficult childhood

Rome public transport are "not so good".
Ok. But how much compared to the other cities?

Where is the better served [by public transport] place in the city?
And in the world?

CityChrone: the context
Urban Accessibility measures

Huge scientific literature

The first definition of accessiblity in urban context is done more than 50 years ago

Many different definitions of accessibility

But no attemp to compute it at large scale.

A science of city needs quantitative measurement

This work must be considered, first of all, as an empirical work. It defines procedures to measure quantities and then we measured them.


Data, algorithms and data visualization.

Quantity Definition

Easy to understand, easy to compute and meaningful quantities to measure public transport efficiency.

Collective creativity

Exploring the huge and complex space of new configurations of the public transport in cities

Data, visualizations, algorithms

Open data sources used

Public Transports Schedules (GTFS format) - transitfeeds

Street graph - OpenStreetMap

Populations data - Eurostat Population Grid, SEDAC

city data and boundary - measuringurban - oecd

DataViz inspirations




Algorithms: routing in urban context

Walking routing algortimh:

New class of public transport routing algorithms:
CSA [2013], RAPTOR [2011]

This new class of algoritms are easy to implements and fast, but they have some crucial limitations in urban context.

We modified the CSA and the RAPTOR algorithm in order to use it in urban context.

Science for City
Boundaries and Tessellation.
It is possible to compute isochrones
First step towards an accessibility measure:
The larger isochrones are, the faster you move.
Velocity Score
Consider the Area of the Isochrone a time \(t\) computed in \(P\): \begin{equation} r(t,P) = \sqrt{\frac{A(t, P)}{\pi}} \end{equation}
dividing by time, we obtain a quantity with the dimension of a velocity:
\begin{equation} v(t,P) = \frac{r(t,P)}{t} \end{equation} Integrating over time: \begin{equation} v_{score}(P) = \int_0^{\infty} v(t, P) f(t) dt, \end{equation} \(f(t)^1\) is the daily time budget distribution for public transport.

The Velocity Score can be consider as the average velocity of a daily typical trip taking a random direction from \(P\).

\(^1\) Robert Kölbl, Dirk Helbing. Energy laws in human travel behaviour. New Journal of Physics 5, 48 IOP Publishing, 2003.
Velocity Score
Average velocity taking a random direction
Paris Rome
... ... ...

interactive maps and more cities:
Sociality Score
Consider the populations inside the Isochrone a time \(t\) computed in \(P\): \begin{equation} s(t,P) = \sum_{i \mid t_i(P) < t} p(h_i), \end{equation}
we sum over all the hexagons with time \(t_i\) less than \(t\) and \(p(h_i)\) is the population within \(h_i\).
\begin{equation} s(P) = \int_0^{\infty} s(t,P)f(t)dt, \end{equation}
\(f(t)^1\) is the daily time budget distribution for public transport.

The Sociality Score quantifies how many citizens it is possible to reach with a daily typical trip starting from \(P\).

\(^1\) Robert Kölbl, Dirk Helbing. Energy laws in human travel behaviour. New Journal of Physics 5, 48 IOP Publishing, 2003.
Sociality Score
Number of people is possible to reach in a typical day trip starting from a point.
Paris Rome
... ... ...

interactive maps and more cities:
City Rankings
City Velocity
Velocity Score per person
City Sociality
Sociality Score per person
City Sociality divided by total population
Values distribution
Area distributions - Population distributions
Inequality distribution of accessibilities
Exponential decay from the center of the city.
Exponential decay of the Velocity Score with the time distance from the center.
Exponential decay from the center of the city.
Exponential decay of the Sociality Score with the time distance from the center.

Why these patterns are observed in all cities?
Are these inequalities unavoidable?

Can be modified or optimized?
In which way?

I don't known.
Interactive platform

Now I know how much Rome public transports suck

What we have to do to reach Paris?

What are the best interventions given a budget?

Let's Play!
Interactive platform for exploring new scenario
Budget: 5 Bilion €
Name Scenario: Gram Author: Pietro
After 1 year
Name Scenario: rer + circle Author: mat
The future of public transports in cities
Bad ending for my current research, but happing ending for public transport in the cities?
Cars per 1000 inhabitants

Italy togheter with USA has the highest level of car ownership.

Italy cars Europe cars
Rome 800 Paris 225
Milan 596 London 298
Turin 600 Barcellona 350
Catania 700 Berlin 297
Average person per car 1.2

95% of the time the cars are parked
Self driving cars (they are around us)
No property - No Parking
Boost in efficency

Sharing Trips
from taxy sharing to trip sharing\(^{1,2,3}\)
At least 50% less cars circulating

Public transport on demand
shrinking of the cost urban transportation of almost 10 times.

1. P. Santi, G. Resta, M. Szell, S. Sobolevsky, S. Strogatz, C. Ratti. Taxi pooling in New York City: a network-based approach to social sharing problems (2013).
2. hubcab
3. shared-mobility-innovation-liveable-cities
Notions - Libraries

Interactive maps: folium

Matrix matlab_style (really fast): numpy

plots: matplotlib

Efficient data analisys: pandas

networks analisys: networkX (easy to use),graph_tools (fast as c++ tools)

need faster computations?: numba(compile python function, fast as c/c++ version)

... more... more

Do you want to make a complex website or app? Take a look to meteor, citychrone is made with it.


The dissemination of the scientific results

Why scientists use a “manuscript” (format invented in late 16th century) to publish and share scientific results, today?


Javascript libraries for interactivity in browsers.

Online communities.

Huge communities, fast deploy results.