The city of Barcelona is cooking up something truly special: a Local Digital Twin (LTD) that resembles a delicious lasagna. Just like how this dish has layers of pasta, cheese, and sauce, the Digital Twin aims to include different layers of systems to create a virtual replica of the city.

Much like the first step of including a solid base when cooking lasagna, Barcelona has replaced the pasta with a virtual representation of the city’s physical reality. “The bottom layer is made up of the map, images of the city, satellite photographs, the street furniture, all the trees, the buildings, the people. It represents the physical world,” explains Jordi Cirera, Director of the Knowledge Society Office of the Barcelona City Council.

But that is not enough. To truly grasp how a city works, you need to throw more ingredients into the mix. This is why the City Council of Barcelona, in collaboration with the Barcelona Supercomputing Centre and the Barcelona Regional agency, has started a new and much more ambitious project. They aim to add new layers to the lasagna, namely the different systems that affect the functioning and behaviour of cities.

“Air pollution and noise monitoring, how goods are distributed throughout the city, traffic management and monitoring, or how people move around, are some of the systems that compose a city model”, notes Cirera. “We want to incorporate these systems and the laws that govern them into the Digital Twin.”

With this comprehensive view of Barcelona, the Local Digital Twin would allow decision makers to run simulations and predict how changes in one system will affect the city. According to Cirera, this technology “will allow the City Council to design, orient and prepare for the Barcelona of the future.”

Digital Twins and the urban planning revolution

Digital Twins are much more than a digital replica of physical systems, people, and environments. They are different from other data analysis and visualisation approaches because they can integrate data from various sources in real time and assess future scenarios through advanced simulations. When applied in urban contexts, DTs can revolutionise how cities approach their management, monitoring, and future planning.

Digital Twins have proven to have many practical applications for cities. Rotterdam, for instance, is building a 3-D city operations platform that allows for the disclosure and visualisation of real-time energy usage data from individual buildings and the entire area.

Flanders, as part of the DUET Digital Twins project, is developing a traffic model that estimates the expected traffic volume in surrounding streets when one or more streets are closed.

The interaction between the traffic model and air quality model allows the simulation of the impact of traffic measures on mobility and the environment. The city of Utrecht is also using a Local Digital Twin, developing an open-source solution that can be adapted to various domains, such as mobility and healthy urban living.

Shaping the city of proximity

Barcelona has developed a ground-breaking Digital Twin platform that serves as a proof of concept and starting point for the city’s ambitious urban planning project. The platform provides a tool to assess whether the city complies with the provision of services or facilities of the city of proximity. The concept is based on the ‘15-minute model’. This term, coined by Paris-based researcher Carlos Moreno, is based on the idea that all essential human needs should be within a 15-minute reach by foot or bike. This means that housing, work, food, health, education, and culture and leisure should be easily accessible to everyone.

Barcelona’s platform analyses the accessibility of public facilities, such as metro stations, hospitals, libraries, or water fountains, among many others. “The platform addresses the six social functions of the 15-minute model, and we could include any data set that the city council has available”, says Cirera. The Digital Twin allows policy makers to evaluate the impact of new construction projects on the city’s infrastructure and assess the accessibility of these facilities to the public. “By including data from the municipal register, for example, we could not only identify areas not covered by the 15-minute model, but also how many people are being left out,” he remarks.

The platform can be replicated in other cities for their own urban planning needs. “Adapting it to other cities and regions should not be too complicated,” acknowledges Jordi Ortuño, Innovation Manager at the Knowledge Society Office of the Barcelona City Council, “it is a matter of changing the map and incorporating the city’s data.” Along with the 15-minute city model, it has many other potential uses. City Councils can include any data set they have available, depending on their intended use of the platform. For instance, they can use it to monitor the location of social and community centres, electric car charging stations, or bicycle racks.

A man on a bicycle on Carrer dels Almogàvers. Photo by Curro Palacios. (Licensed under CC BY 4.0)

Building a city-wide modelling programme

The Digital Twin of Barcelona is set to become even more complex as it moves into its next phase. Just like adding layers to a lasagna, the project aims to add new levels of complexity that incorporate the many different systems that intervene in city planning.

“During the first phase, known as the 15-minute platform, we have created a digital copy of the city of Barcelona, representing a highly detailed but static photograph”, mentions Ortuño. The platform is the result of the first phase of an ambitious project in which the City Council has worked closely with researchers from the Barcelona Supercomputing centre.

Now, they are launching a second stage, aimed at creating a city-wide modelling programme. The model aims to reproduce how different physical, social, and digital systems impact each other and the city.

Introducing a small change in the choice of ingredients for the lasagna -for example, sugar instead of salt – results in a quite different dish. The same is true for city systems. When this phase of the project is completed, the Digital Twin would be able to assess, for example, how changes on citizens’ employment patterns affect the level of traffic and, therefore, air pollution levels, or how closing a street can affect noise levels in neighbouring areas.

By adding these systems and the rules that govern them, the model will be able to provide city planners with a deeper understanding of how the different systems interact with each other, enabling them to make more informed decisions that will have a positive impact on the city.

However, such a complex project will require a significant amount of time to complete. The municipalities of Bologna and Barcelona, together with the Barcelona Supercomputing Center (BSC-CNS) and the CINECA Consortium of Universities, are defining the milestones to be completed during the development of this initiative. The current objective is to define concretely what collaborations and joint projects will be developed during this phase within a European framework.

One of the biggest challenges they will face is understanding the rules that govern these systems, as they are often incredibly complex and not well understood. “We aim to have a record of data for systems whose laws are unclear. The goal is to use an artificial intelligence system to infer or approximate the outcomes,” discloses Cirera.

A shared culture on Digital Twins

Although the concept of the Local Digital Twin is something new, the idea behind this technology has been around for a long time. “Ultimately, such tools are not about inventing anything new,” points Cirera. “It is about answering four fundamental questions that we have been asking ourselves for a long time: What has happened, what is happening now, what will happen in the future, and what if something were to change?”

The development of the Barcelona LDT highlights the critical role that collaboration between cities and organisations plays in achieving ambitious goals. The project would not have been possible without the agreement between Barcelona and Bologna, who teamed up with two of Europe’s most powerful supercomputers: the Barcelona Supercomputing Center (BSC-CNS) and the CINECA Consortium of Universities, which includes the University of Bologna. By combining resources and expertise, these partners were able to push the boundaries of what was possible. This serves as a reminder that collaboration is essential to developing large-scale projects and achieving significant breakthroughs.

As more and more EU cities begin to adopt Local Digital Twins (LDTs), the potential benefits of this cutting-edge technology are becoming increasingly clear. To ensure that as many cities and communities as possible can take advantage of LDTs, and to foster a fair and innovative European digital twin market, Ortuño defends that “ensuring spaces for working together, sharing knowledge and best practices is essential.”

In this sense, the Living-in.eu community has set up a specific forum on Local Digital Twins. Thanks to the collaboration between city, regional and national experts, the Living-in.EU comunity aims to identify existing use cases and potential interest from different groups across the EU. The European Commission has launched funding calls to develop an EU LDT Toolbox, which will provide cities with re-usable tools, reference architectures, open standards, and technical specifications. Furthermore, the Eurocities Task Force on Digital Twins worked last year to promote a culture of Digital Twins, in which smart cities can share experiences, knowledge, initiatives, best practices and harmonise strategies. All these measures aim to enable interoperability, facilitate the creation of a network of LDTs, and spur innovation among European cities and communities.