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Inf@Vis!

The digital magazine of InfoVis.net

Visualising the Pulse of the City
by Fabien Girardin [message nº 190]

In this issue, we present the emerging opportunities to use geovisualizations to reveal the "pulse of a city" with the visualization of spatio-temporal data generated by the people's experience of systems to interact with the urban environment.

In recent years, the large deployment of mobile and wireless technologies has provided new means to understand the dynamics of a city. They bring new perspectives for urban planners, traffic engineers, tourism authorities in addition to the  traditional urban data collection methods such as counting the traffic at crossroads or surveys by person or phone.

In our every day activities we leave behind footprints from our interaction with the urban environment and its digital infrastructures (e.g. taking and sharing digital photos, communicating through wireless networks, withdrawing money). 

These footprints can be added to the other signs people leave in urban environments such as stickers, rubbish, footsteps or graffiti. From these clues, other people can draw a large range of inferences: others were here, this was popular, where I can find something, or where shouldn't I go

While the collection of these digital footprints poses serious privacy issues, it also opens up unprecedented opportunities to reveal the dynamics in urban environments.

Pioneer projects showcased the mapping and visualization of mobile phone usage to represent the urban activities and their evolution through space and time. In their Real-time Rome project, the MIT SENSEable City lab developed different processing and visual software to explore how researchers might be able to use data for an entire metropolitan region. 

They were able to reveal 6 main themes:

RealTimeRome-MadonnaConcert.jpeg (214589 bytes)
Figure 1: Madonna's concert. 
Source: MIT SENSEable City Lab
  • Pulse: Where in Rome are people converging over the course of a day?

  • Gatherings: How do people occupy and move through certain areas of the city during special events?

  • Icons: Which landmarks in Rome attract the most people?

  • Visitors: Where are the concentrations of foreigners in Rome?

  • Connectivity: Is public transportation where the people are? How do the movement patterns of buses, taxis and pedestrians overlap?

  • Flow: Where is traffic moving?

In a proof of concept, their software visualized the pre-recorded intensity of mobile phone usage during important events in Rome such as the celebration of the winning of the World Cup by the Italian national team or the Madonna concert [figure 1] (video).

However, the telecommunications industry is seldomly queen in sharing its data access, partially because they must comply with strong governmental directives on personal data and the protection of privacy. The aggregated GSM network data they disclose reveal mobility patterns of crowds but leave other facets of the city invisible.

As a consequence, other scholars have explored new means of collecting data to reflect human activity and its consequences (e.g. pollution, traffic jams). These types of  projects have been stimulated by the arrival of Google Earth and its democratization effect on Geo-Data visualization. It quickly became a popular platform for overlaying data to communicate key issues to the public at large.

For instance, mobile devices such as the ones used in the Urban Pollution Monitoring Project allow people to explore a city area while collaboratively visualizing carbon monoxide in real-time. Their usage creates an improved understanding of the pollution phenomenon on the street as mapped, in another project, by the 3-D Map of Air Pollution in London [Figure 2b]. Similarly, Bio-mapping aim at revealing a qualitative view of a city through communal emotion maps generated by people wearing a device which records the emotional arousal in conjunction with their geographical location [Figure 2a].

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Figure 2: (a) Bio-mapping, the tool reveals the increase of emotional arousal at a busy traffic crossing. (b) An interactive three-dimensional map that allows users to "fly" above London to see pollution hotspots by the Centre for Advanced Spatial Analysis (CASA) - University College London and King's College.

Yet, in most cases, mere data is not enough, and the development of ad-hoc software and systems in partnership with telecomunication or urban infrastructure companies is required. As a consequence, other approaches collect and analyze the history of physical presence of individuals from the digital footprints they publicly make available on the world-wide web. 

For instance the Tracing the Visitor's Eye project retrieved from Flickr, large amounts of photos taken by thousands of users in the world’s most photographed cities. Based on the time, explicit location and people’s description of their photos, geovisualizations reveal the tourist activity and flows in space and time. More specificaly, they provide insights into the density of residents and tourists in an area [Figure 3] as well as on the flow and activity of tourists within [Figure 4], in and on that area.

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Figure 3: Tourist Density. The mapping of the georeferenced photos publicly available in Flickr reveal the density of tourists in downtown Barcelona in 2006.
Source: Fabien Girardin, Universitat Pompeu Fabra
Figure 4: Traces left by Flickr users in and around the Tuscany region in Italy. Practically, a trace consists of a chronologically ordered set of geographically referenced photos taken by one person over the course of one day. Aggregating these personal traces reveal the travel behavior of specific types of visitors. For instance, the visualization on the left reveals that Americans follow a specific graph constituted by the nodes of Florence, Siena, Pisa, Genova and Perugia. On the other hand, Italians (right) are more adventurous in their exploration of the area (including reporting on visits of the Island of Elba). 
Source: Fabien Girardin, Universitat Pompeu Fabra

All this project strongly suggests that the analysis and visualization of the spatio-temporal data can derive valuable high-level human behavior information in realms of urban planning, mobility, social interactions or consumer behavior. Moreover, this information becomes very interesting when returned to people to help them make more informed decisions about their environment. 

A few weeks ago in Rome, the MIT SENSEable City Lab closed this feedback loop as a first instantiation of their Wikicity project. They aggregated various types of data and visually mapped the density and movement of people, buses, taxis, events in real time throughout the whole of the Eternal City. By revealing the pulse of the city, the project aimed to show how technology can provide the inhabitants with a better idea of their own city and can help adjust their behavior accordingly.

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Figure 5: Give the data back to the community. WikiCity project in Rome. 
Source: MIT SENSEable City Lab

However, providing a proper mirror on the urban activity raises several challenges. First a vital element of such a system will be the protection of contributors’ privacy. Second, in many cases the visualizations emerge from incomplete data with fluctuating accuracy. The effectivity and relevance of these geospatial visualizations strongly depend on the approaches to successfuly integrate the uncertainty of the source data.


1. In Europe, there is the 2002 Directive by the European Parliament and Council on privacy: Directive 2002/58/EC of the European Parliament and of the Council of 12 July 2002 concerning the processing of personal data and the protection of privacy in the electronic communication sector (Directive on privacy and electronic communications).

Meet the author:

Fabien Girardin is a Ph.D. candidate in Computer Science and Digital Communication in the Interactive Technologies Group at the Universitat Pompeu Fabra (UPF) in Barcelona, Spain. He is also affiliated to the Senseable City Lab at the Massachusetts Institute of Technology (MIT) in Boston, USA. His current investigation explores the integration of ubiquitous technologies in the everyday urban environments.

Previously, he was a member of the CRAFT at the Swiss Federal Institute of Technologies, Lausanne (EPFL)  to design, implement, and study location-aware collaborative applications. Subsequently, Fabien co-founded Simpliquity, an EPFL spin-off that offers user experience consultancy in the domain of emerging technologies.

After a conversation about his work in Barcelona Fabien kindly agreed to contribute this interesting article about the visualisation of the pulse of the cities.

Links of this issue:

http://www.amazon.com/Putting-People-Map-Confidentiality-Social-Spatial/dp/0309104149   The book Putting People on the Map
http://senseable.mit.edu/realtimerome/   Real Time Rome
http://senseable.mit.edu/   The Senseable City Lab at MIT
http://senseable.mit.edu/realtimerome/sketches/movies/wmv/s6.wmv   Video on Real Time Rome
http://earth.google.com/   Google Earth in English
http://www.equator.ac.uk/index.php/articles/563   Urban Pollution Monitoring Project
http://www.londonair.org.uk/london/asp/virtualmaps.asp   3D Map of London pollution
http://biomapping.net/   Biomapping
http://www.girardin.org/fabien/tracing/   Tracing the Visitor's Eye
http://www.flickr.com/   Flickr website
http://senseable.mit.edu/wikicity/rome/   Rome Wiki City/strong>
http://senseable.mit.edu/wikicity/   MIT Senseable City Lab WikiCity project
http://www.girardin.org/fabien/   Fabien Girardin personal page
http://gti.upf.edu/   Interactive Technologies Group at UPF
http://craft.epfl.ch   EPFLs Center for Research And support oF Training
http://www.simpliquity.com   Simpliquity
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