# Citychrone Platforms: quantities description, open data and algorithms.

## CityChrone platform - Science for City, Citizen for Science.

The CityChrone Platform has two principal objectives: the first one is to contribute to base on quantitative studies the science of city. The second one is to allow users and citizen to participate in finding new and creative solution to public transport problems in city.

### Science for City

The CityChrone project study the quality of the services of the public transport in cities. The CityChrone platform shows simple and meaningful quantities to measure the quality and the performance of public transport in cities. It allow to answer questions like: ”Which zone of the city is well served by pubic transport?”. ”How much the public transport of Paris differ with those of Rome?”. The CityChrone Project aims to give quantitative measure of cities, it is intended as a theoretical as well as ”experimental” work to help in basing the emergent field of the ”New Science of City”\ref{batty2013new}. Moreover the measures will be presented in a interactive and user-friendly platform that allows the more vast audience to understand and reuse the results. The data produced as well as the code used will be freely downloadable from open-source platform, allowing scientist, institution and citizen use it.

### Citizen for Science

The second part of the project calls users of the platform to play in order to solve very difficult scientific and society issue. The problem which users will face off is finding new public transport scenario in order to optimize the quality measure described above. For specific cities there is a section called ”new Scenario” where it is possible, constraint to a limited budget, add new metro lines to the city and see, in nearly real time, how change the public transport services in the city. The platform uses the intellectual ability of users to explore the huge space of possible new subways scenario, impossible to explore by brute-force algorithms. At the end of each new configuration tested the position in the ranking of the scenario is shown enhancing the gamification aspect of the platform.

## Quantities definition:

In the next subsections we define the quantities that measure the quality of public transport services in cities shown in citychrone.org. We start from the isochrone layers, prerequisite to understand the other quantities: Velocity Score and the Sociality Score.

### Isochrone

An isochrone at time $$t$$ is the surface at equal time distance from a starting points. In the layer ”isochrones” in citychrone.org the isochrones, computed by public transports are shown. In fig.1 is shown the public transport isochrones in New York city, every $$15m$$ from a starting point in Manhattan. On the citychrone.org is possible to explores the isochrones of the cities, clicking on the map so to change the starting point.