# Collecting, Processing and Secondary Using Personal and (Pseudo)Anonymized Data in Smart Cities
## 1 Introduction
Customers have for decades entrusted organizations with their personal information, assuming they will use them to enable better and new services while enhancing the company's decision-making. In recent decades, data collection and intensive processing has accelerated exponentially, enabled by novel communication and processing technologies [4], creating new business areas based on user-related data. Today, data aggregators or brokers range from clear examples such as wide-range private companies (e.g., Google, Amazon, Twitter or Facebook) and government agencies to not-so-clear examples such as our health insurance company or bank. Even if the main activity is not data collection and processing, they all claim ownership and exploitation rights over other people's data. From the data brokers' perspective, consumer data is valuable to businesses and the consumer profile is gold. There are plenty of companies that would love to discover where we shop online, our political preferences, what websites we used to visit, where and how much we spend, our medical history, our lifestyle, in short everything about the consumer. Of course, all this information about users is not always used in abusive transactions but could also be instrumental in helping third-party analysts and investigators answer queries ranging from urban planning [5; 6] to treating and curing diseases [7; 8; 9; 10]. Even for these legitimate transactions, companies often want to share this information with other parties without compromising the confidentiality of their customers. Back to the smart cities context, the issue is how to enable the primary and secondary use of the mass of data collected by the different sources and distinct formats in the city without eroding citizens' privacy. The risk of social and economic damage due to the exposure of personal or sensitive information, confirmed by reported abuses in the use of personal data and data breaches, has increased so fast that it has led civil society to demand more protection and guarantees about the privacy of their data, in addition to stricter rules on the collection and processing of this data. As a clear response, several legislations have emerged worldwide to regulate the use of this data and guarantee the individual'sright to privacy. In common, they consider anonymization and pseudonymization as proper technical solutions to obtain the benefits of the secondary use of personal data but without any prejudice to the privacy of individuals. In Europe, the General Data Protection Regulation (GDPR) imposes a uniform data security law on all EU members. With the approach of privacy being a fundamental right, there is a need to review how user data is used and handled by organizations and businesses [11], and cities. Anything that could identify a person, from IP addresses to a digital print [12], is now under protection. GDPR defines personal data as any data of an identified or, at least, identifiable individual--which includes name, email, geolocation, IP address, and also sensitive data related to health or that reveals ethnicity, racial origin or sexual orientation. Even images can be considered personal data, whenever footage or images can be used to directly or indirectly identify an individual. The risk of re-identification and de-anonymization are critical privacy issues in the development of a smart city. Choosing the right de-identification, anonymization or pseudonymization technique or solution is crucial in ensuring the protection of sensitive information. Once a dataset is made public, it becomes vulnerable to future information releases that could potentially lead to re-identification.