**Preface to "Sustainability and Visitor Management in Tourist Historic Cities"**

From a cultural point of view, historic cities have a secular legacy that expresses the basis of the community's identity, while, from an economic perspective, they are linked to the consideration of heritage and culture as drivers of development [1]. In this sense, historic cities are major tourist attractions that lead to an influx of visitors, which threatens their sustainability [2–4]. G. J. Ashworth and J. E. Tunbridge [5] developed the concept of tourist historic cities (THCs) as areas in which urban structure, architecture, and artifacts are used to create heritage assets that are based on place. Historic cities are also "convergent spaces": They lead to coinciding social behaviors, as various activities take place within their "borders".

Tourist activity is continually increasing in tourist historic cities. It contributes to local and regional economic development but also creates significant social and environmental problems that are heightened by the increase in the population living in these spaces. Sustainable practices are key factors in reaching balanced economic, social, and environmental development. The concept of sustainable tourism management means regulating and controlling the rate of growth within a destination [6–9]. However, putting sustainability into practice is a complex process, due to the lack of practical tools for measuring the impacts of tourism in all their dimensions. In fact, UNWTO launched the Measuring Sustainable Tourism (MST) project to develop an international statistical framework for measuring the economic, environmental, and social sustainability of tourism. As new sources of data for the analysis of tourism have emerged, this initiative calls for a framework that is based not on the use of traditional data sources but one capable of using and integrating all possible sources to provide the richest picture possible [10]. In this context, Tourist Information Systems or Tourist Observatories must be encouraged as tools for unifying all data sources and establishing a systematic way to monitor tourism indicators that can guide decision-making processes and promote smart cities [11,12].

Challenging and innovative management measures leading to favorable dynamics are required to pave the way for a discourse of socially-sustainable tourism practices [13,14]. Therefore, all public and private territorial actors involved in tourism must work together to integrate cultural, tourism, and urban policies [15–17]. In addition, the participation of local residents in decision-making processes is one of the most widely discussed parameters in debates on the preservation and sustainability of tourism management [16,18,19]. Nevertheless, because the public has not been involved in developing tourism strategies, public administrations are dealing with social conflicts and movements that protest the 'touristification' of public spaces, the increased cost of rented housing, the loss of traditional commerce, and other problems. It urges a collective, consensual choice based on the principles of commons creation and governance, care, and conviviality [9].

Taking into account this scenario, the purpose of this Special Issue is to identify new trends and tools in measuring, planning, and managing sustainability and visitor flows in historic cities. It includes seven articles that cover new approaches to studying tourism impacts, historical city management, visitor movement, and tourism sustainability through one literature review and six case studies in the historic cities of Seville and Toledo (Spain), Venice and Matera (Italy), Porto (Portugal), and Popayán (Colombia).

In the first article Carmen Mínguez, María José Piñeira, and Alfonso Fernández-Tabales investigate the impacts of tourism activity by introducing the concepts of physical, environmental, economic, residential, and social vulnerability to which historic cities and their population are exposed when dealing with tourism. They present a practical and applied example of how to measure the degree of vulnerability and how to analyze the social and spatial effects of tourist activity in the historic city of Seville, a consolidated destination in Southern Spain, and also the third-ranking Spanish city in tourism activity after Madrid and Barcelona. For this reason, an urban vulnerability indicator is designed and tested based on a combination of demographic, social, economic, and housing variables, such as population by age, number of unemployed, working-age population, rental prices, and number of rental housing ads. Results show that tourist areas of the historic center of Seville have the highest vulnerability, while less attractive areas for tourists have the lowest vulnerability and do not lose population. This innovative method contributes a quantitative and statistical treatment of a phenomenon that until now had been studied through qualitative or descriptive approach or with less detail at the scale of spatial breakdown.

The second article authored by Inês Gusman, Pedro Chamusca, José Fernandes, and Jorge Pinto addresses the case study of Porto, the second-largest Portuguese city and World Heritage Site, which, in the last 20 years, has experienced significant tourism growth. In this research, the impacts of tourism are also measured through indicators related to tourism, housing, and economic activity, but the main aim is to assess tourist impacts on the cultural value of the city. The contribution of this work is relevant considering the current threats that cultural sustainability is facing because of the growing interest in cultural tourism, which encompasses over 39% of total international tourism arrivals [20]. The results highlight the prevalence of spaces characterized by excessive tourism activity, a loss of the residential function, and overexploitation of cultural values. In this sense, authors noticed an increase of short-term rentals and real state value, as well as a commerce transformation to reinforce services oriented towards visitors, such as the emergence of self-service laundries and souvenirs shops or changes in traditional markets to satisfy tourist needs. The article also advances some policy recommendations to promote strategies oriented towards maintaining cultural values of historic cities, not only as a way to keep a sense of identity and belongingness for the residents, but also because living cultures, value systems, beliefs, and traditions are more and more appreciated by visitors [21].

Dario Bertocchi and Francesco Visentin study the physical and social effects of massive tourism in the historic city of Venice, a very significant case study as it is one of the best examples of overtourism and anti-tourism movements. The authors begin with a description of the current situation of Venice in terms of touristification, especially referring to the social conflicts generated in the society because of the existence of different interests in relation to tourism. A mixed methodology is applied to understand urban transformations that occurred in Venice between 2008 and 2019. A quantitative analysis is developed to study the physicalfacility capacity through the application of indicators provided by the UNWTO Measuring the Sustainable Tourism report (MST), such as number and type of tourism facilities, number of residents, and number of tourists. Besides, a qualitative approach is used to collect 6,272 opinions from inhabitants of the historical center of Venice that can assess the social-perceptual capacity. As also noted by I. Gusman et al. in the case study of Porto, commercial and residential structures have significantly changed to adapt to tourist needs. This issue is critical in Venice where inhabitants are more and more intolerant with uncontrolled mass tourism, leading to social movements that demand the involvement of Venice's residents in tourism planning. D. Bertocchi and F. Visentin conclude with recommendations to policymakers to regulate some issues, for example, in the food and beverage sector, accommodation in Airbnbs, and tourism flows, as well as to reactivate other urban ecosystems, services, and uses beyond tourism.

Knowledge of the opinions of host communities is essential to measure tourism impacts, as D. Bertocchi and F. Visentin address in the case study of Venice. The fourth article of this book provides another experience to understand resident opinions and perceptions of destinations in historic cities. This is the research carried out by Luis Escudero in the historic center of Toledo, which is one of the main cultural tourist destinations in Spain, 75 km south of the capital of the country, Madrid. A quantitative survey is applied to 442 residents and the results are analyzed using descriptive and analytical statistics (factor analysis and nonparametric tests). Findings show an optimistic vision of tourism development, specifically the creation of jobs, although residents also express the feeling of turning the city into a museum, an increase in traffic flow, and pedestrian congestion. They do not consider that tourism affects the cultural heritage or the use of Toledo by the residents. In addition, demographic and socioeconomic characteristics influence the residents' opinions. For example, residents in the historic center have a more negative opinion of tourism than those who live in other residential areas, and homeowners scored tourism development higher than renters. This paper highlights the need for policymakers to understand resident perspectives to get the support of the local community to develop tourism activities while reducing tourism negative impacts.

Information sources to measure tourism impacts have evolved from traditional sources (questionnaires, interviews, and direct observations) to new sources, such as big data technology, which include store cashiers, mobile network operators, social media, web activity, flight reservation systems, financial transactions, traffic loops, satellite images, etc. [22]. In the fifth article, Yamilé Pérez-Guilarte and Daniel Barreiro present a literature review to survey and describe the current main approaches and methodologies to use big data to produce official tourism statistics that support destination management organizations. The research is specially focused on how to measure social, economic, and environmental sustainability. The methodology used is the Systematic Literature Review (SLR) technique. Papers published in Web of Science (WOS) and SCOPUS databases between 1999 and 2019 are examined, together with publications from international and European organizations. The authors highlight that only ten of a potential 180 papers refer to the use of big data in tourist statistics, which demonstrates that research in this field is still relatively new. Wikipedia, Facebook, Twitter, or Instagram and geotagged photos data from Flickr are the most common sources of data. Besides, the traditional separation between academia, public authorities, tourist companies, and technological centers is evident, as half of the initiatives to create tourist information systems using big data came from an academic environment. This paper proves that big data can cover the traditional gap of measuring tourism sustainability by proposing indicators, especially those with geographical and temporal granularity.

In the sixth article, Ana Muñoz-Mazón, Laura Fuentes-Moraleda, Angela Chantre-Astaiza, and Marlon-Felipe Burbano-Fernandez compare the use of traditional information sources (questionnaires) with technological ones, specifically tourist cards, global positioning system (GPS), and near field communication (NFC). The objective of the study is to determine the most precise method to obtain data on tourist movement in the historic city of Popayán. The city is located in the south of Colombia, 596 km from Bogota D.C with a cultural tourist vocation, but is still in the phase of tourist development. Each tool is applied during the Holy Week of the 2011 (tourist card), 2012 (survey), 2013 (GPS), and 2015 (NFC). A total of 1,346 movements are recorded in the 36 resources identified within the tourist offer. For the research, a combination of tools such as GPS Visualizer tool, Google Maps, and R statistical software, and descriptive analyses are used. The results indicate that questionnaires require a lower technological infrastructure, but, on the contrary, they depend on tourists' willingness to answer the questions, and in their ability to remember visited sites at the destination. The tourist card can collect tourist profiles and the exact date and hour of their visit to the different tourist attractions. GPS technology provides the most accurate results. However, NFC technology offers more extensive information, thus allowing the extraction of data about the visited sites. The paper contributes to a better understanding of the different tools to study tourist movements and encourages destination management organizations to make the most of these tools to improve tourism planning and management.

Finally, in the seventh and last article Antonietta Ivona, Antonella Rinella, and Francesca Rinella adopt a historical perspective based on a qualitative and interpretative methodology and the use of information and communication technologies. The research addresses the "virtual" territorial reconfiguration developed in the Italian Southern city of Matera, also socalled "Città dei Sassi" (The City of the Stones) due to its morphology and peculiar urban landscape. Specifically, the authors analyze the territorial impacts that an important cultural event, such as the appointment as the European Capital of Culture 2019, has on the city. In this case, the main focus of interest is the tourist historic city proper, highlighting that, despite its troubled history, the city of Matera was able to transform "The Sassi" (The Stones), originally considered as a "national shame", into the international urban identification for the 2019 European Capital of Culture. In contrast to the other case studies, such as Seville, Porto, and Venice, Matera is a smaller city whose strength resides in being a proper example of a resilient city that has decided to take advantage of its unique urban-caved landscape to claim its localization on the international map. The inevitable and necessary recovery of the "hard city" that has been taking place since the 1960s, as well as the following tourist and international promotion enhanced by its UNESCO World Heritage since 1993, are being associated with a post-contemporary "soft city". In this last case, local stakeholders and residents cooperate to foster bottom-up territorial planning that finds its virtual space on the world wide web. Apart from highlighting the beginning of the virtual territorial reconfiguration of a historic city, this article underlines how content produced and diffused by stakeholders engenders a renewal of the symbolic, material, and organizational realities of group municipalities, so that they can function as a connected network to promote sustainable tourism.

This book is expected to support tourism destination organizations with practical tools to measure social, environmental, and cultural tourism impacts, thus promoting sustainable management of tourist historic cities. In addition, the authors strongly hope that the methodologies, findings, and discussions presented in their papers and collected in the book encourage further research committed to theoretical and empirical studies.

**Conflicts of Interest**: The authors declare no conflict of interest.

#### **Rubén Camilo Lois González, Yamilé Pérez Guilarte, Lucrezia Lopez**

*Guest Editors* 

#### **References**

