Geomorphological mapping in urban areas

Research into urban geomorphology is relatively recent (Brown et al., 2017; Rosenbaum et al., 2003; Zwoliński et al., 2017), and the discipline is gaining interest at an accelerating pace, as global research communities become aware of the increasing intertwinement of geomorphological and anthropogenic forces, and their interrelated effects on urban life and urban form. Rapidly advancing disciplinary insights demand for continuous renewal, updating and assessment of the discipline’s methods, techniques and approaches to recognizing and mapping landforms, processes and deposits in urban environments (Brandolini et al., 2019; Del Monte et al., 2016; Diao, 1996; Ferrando et al., 2021; Zwoliński et al., 2018). Indeed, geomorphological surveys in urban areas involve careful observations of morphology, particularly at the medium-large scale (Bathrellos, 2007; Eyles, 1997; Faccini et al., 2008). Additionally, insights from other sources, particularly historical and geographical documents as well as excavation and borehole data, are essential in order to identify, map and date landforms and deposits (Brandolini et al., 2018; Giardino et al., 2015; Lucchetti & Giardino, 2015). This process is particularly difficult due to the stratification of urban expansion phases (Luberti, 2018; 2019). In Europe these cities were often founded in historical times, expanded in the Middle Ages and progressively grew larger (Del Monte et al., 2013; Zwoliński et al., 2018), and entered a period of uncontrolled urban sprawl in the 20th century, and particularly after the Second World War, partly related to the development of the second houses, rural and suburban lifestyle, and tourism (Brandolini et al., 2017; Edgeworth et al., 2015). Moreover, changes in the earth’s surface morphology lead to significant transformations of the urban space, forms are created as a result of artificial works and natural denudation and accumulation processes. In effect, there are also hybrid forms, negative and positive forms, concave and convex forms. Anthropogenic forms and deposits can both enrich and impoverish the complex morphological landscape and natural geodiversity of cities. The fundamental basis of this special issue, is the capacity of urban geomorphological research to generate new insights into the effects of urban growth on geomorphological processes and landforms and vice versa, and their relationship to increasing geological risks (Mandarino et al., 2021), In addition, the dissemination of cultural geoheritage in urban areas must also be addressed (Pica et al., 2018; Reynard et al., 2017; Thornbush & Allen, 2018). Promoted within the initiatives carried out by the Working Group on Urban Geomorphology of the International Association of Geomorphologist (IAG), this Special Issue is devoted to geomorphological surveying and mapping applications in urban areas, addressed at highlighting the topographic features and geographical-physical conditions that drove the choice of settlement and subsequent urban development, as well as to evaluating the impacts of human intervention on geomorphological processes and landforms. This Special Issue, collecting twenty-four case studies from around the world, offers an opportunity to share knowledge about geomorphological processes in urban areas and to prompt such debate, creating a gathering point for researchers and practitioners who deal with land planning and land management of risk mitigation measures as well as with the preservation and management of geocultural heritage, in a variety of morphodynamic and climatic contexts.

a Genoa University, Genoa, Italy; b Sapienza University of Rome, Rome, Italy; c Delft University of Technology, Delft, Netherlands; d Adam Mickiewicz University, Poznań, Poland; e Ulster University, Belfast, UK

Background
Research into urban geomorphology is relatively recent (Brown et al., 2017;Rosenbaum et al., 2003;Zwoliński et al., 2017), and the discipline is gaining interest at an accelerating pace, as global research communities become aware of the increasing intertwinement of geomorphological and anthropogenic forces, and their interrelated effects on urban life and urban form.
Rapidly advancing disciplinary insights demand for continuous renewal, updating and assessment of the discipline's methods, techniques and approaches to recognizing and mapping landforms, processes and deposits in urban environments (Brandolini et al., 2019;Del Monte et al., 2016;Diao, 1996;Ferrando et al., 2021;Zwoliński et al., 2018). Indeed, geomorphological surveys in urban areas involve careful observations of morphology, particularly at the medium-large scale (Bathrellos, 2007;Eyles, 1997;Faccini et al., 2008). Additionally, insights from other sources, particularly historical and geographical documents as well as excavation and borehole data, are essential in order to identify, map and date landforms and deposits (Brandolini et al., 2018;Giardino et al., 2015;Lucchetti & Giardino, 2015). This process is particularly difficult due to the stratification of urban expansion phases (Luberti, 2018;. In Europe these cities were often founded in historical times, expanded in the Middle Ages and progressively grew larger (Del Monte et al., 2013;Zwoliński et al., 2018), and entered a period of uncontrolled urban sprawl in the 20th century, and particularly after the Second World War, partly related to the development of the second houses, rural and suburban lifestyle, and tourism (Brandolini et al., 2017;Edgeworth et al., 2015). Moreover, changes in the earth's surface morphology lead to significant transformations of the urban space, forms are created as a result of artificial works and natural denudation and accumulation processes. In effect, there are also hybrid forms, negative and positive forms, concave and convex forms. Anthropogenic forms and deposits can both enrich and impoverish the complex morphological landscape and natural geodiversity of cities.
The fundamental basis of this special issue, is the capacity of urban geomorphological research to generate new insights into the effects of urban growth on geomorphological processes and landforms and vice versa, and their relationship to increasing geological risks (Mandarino et al., 2021), In addition, the dissemination of cultural geoheritage in urban areas must also be addressed (Pica et al., 2018;Reynard et al., 2017;Thornbush & Allen, 2018). Promoted within the initiatives carried out by the Working Group on Urban Geomorphology of the International Association of Geomorphologist (IAG), this Special Issue is devoted to geomorphological surveying and mapping applications in urban areas, addressed at highlighting the topographic features and geographical-physical conditions that drove the choice of settlement and subsequent urban development, as well as to evaluating the impacts of human intervention on geomorphological processes and landforms.
This Special Issue, collecting twenty-four case studies from around the world, offers an opportunity to share knowledge about geomorphological processes in urban areas and to prompt such debate, creating a gathering point for researchers and practitioners who deal with land planning and land management of risk mitigation measures as well as with the preservation and management of geocultural heritage, in a variety of morphodynamic and climatic contexts.

Overview of the papers in this special issue
The contributions, within the framework of the general theme "Geomorphological mapping in urban areas", addressed the following main topics: . detection of geomorphological features driving the choice of settlements and subsequent development of urban towns; . evaluation of the modifications and impacts of human intervention on geomorphological processes and landforms in urban areas; . definition and selection of methods for geomorphological survey and mapping in urban areas; . analysis of the geomorphological changes in urban areas and their relationships with archaeological and historical data; . evaluation and mapping of geomorphological hazard/risk in urban areas to support planning and management of mitigation measures; . promotion of geoheritage and geotourism in urban areas.
Original research in different geographical areas, mainly in the European Mediterranean region and Central Europe, and secondarily in Africa and North America was presented. Within some of the major urban areas in Italy, seven interesting case studies presented geomorphological maps of Rome (Vergari et al., 2020), Naples (Ascione et al., 2020), Alessandria , Pavia , Palermo (Cappadonia et al., 2020), in Genoa  and Cagliari (Porta et al., 2020). These contributions pay particular attention to the application of the new geomorphological legend proposed by ISPRA/AIGeo (Campobasso et al., 2018), that was tested in different morphodynamic contexts, both coastal and fluvial. Still among Italy's big cities, Turin (NW Italy) is also presented, highlighting the mapping of alluvial terraces as evidence of the Holocene evolution of the River Po (Forno & Gianotti, 2020).
Two case studies deal with tourist cities representative of the Eastern Liguria Sea (NW Italy) such as Rapallo  and Chiavari-Lavagna (Roccati et al., 2020), whose coastal floodplains have been mapped with the aim of supporting urban area management, and highlighting the anthropogenic landforms that have increased geo-hydrological and coastal hazards.
Another coastal case study, relates to Rimini in the North Adriatic Sea (NE Italy), highlighting the factors which influenced the historical evolution of the town, relating them to anthropogenic features, with maximum peaks in natural changes probably matching periods of climate deterioration (Guerra et al., 2020).
Two maps presented for the central-southern Apennines (Italy), concern the exposure to landslides and the relationship of the spatio-temporal distribution of landslides to urban development in the urban centers of Castelsantangelo sul Nera in the Marche , Volturino and Motta Montecorvino in Apulia (Zumpano et al., 2020). The insightful case study of the city of Isernia (southern Italy) illustrates the relationships between landscape evolution and human occupation since the Middle Pleistocene, integrating geological-geomorphological investigation with archaeological data .
In Central Europe, within the Bohemia region (Czech Republic), the disappearance or modification of former man-made landforms has been studied, reviewing the transformation of ponds following industrial and agricultural activities (Frajer et al., 2020). The stages of the digital adaptation of the printed version of old geomorphological maps are discussed for the Upper Silesian industrial region (Szypuła, 2020).
Other five impressive case studies have been presented from Poland: the city of Torun has been studied by historical comparison of multitemporal maps from XVIII century as a significant case of disappearing features of the cultural landscape due to anthropogenic degradation of dunes within the city (Molewski, 2020); the city of Warsaw with the reconstruction of urban geomorphology of the Vistula River Valley using an ALS LIDAR DEM to map complex landforms with implications for flood management, geoarchaeology, and geoheritage conservation (Wierzbicki et al., 2021); the Krakow city center, where the changes in topography during the last millennium have been analysed using reconstructed paleotopography and urban archeology (Łajczak et al., 2020); the city of Wałbrzych representing a geomorphic landscape, heavily modified by nearly three centuries of industrial activity, related mainly to coal mining (Jancewicz et al., 2020); the city of Poznań by the mapping of geohazards (e.g. river floods, flash floods, mass movement, wind erosion) specific to an urban lowland area because of increasing climate change (Zwoliński et al., 2021).
In the African continent, two significant projects in the agglomeration of Antananarivo in Madagascar (Frodella et al., 2020) and Karthum in Sudan (Zerboni et al., 2020) were conducted, addressing aspects of urban geology and geomorphology, as well as geohydrological hazards in relation to an outstanding cultural and archaeological heritage.
Finally, an innovative contribution concerning the city of Vienna in Virginia (North America), located about 12 miles west of Washington D.C., focusing on geomorphological mapping and anthropogenic landform change in an urbanizing watershed using Structure-from-Motion photogrammetry and geospatial modeling techniques (Chirico et al., 2020).

Final remarks
The studies collected in this Special Issue summarize many interesting environmental and geocultural issues that can occur in urban areas, providing new perspectives and developments within geomorphological mapping both for scientific and applied cartographic practice and research. They explore methods and techniques concerning how to map, monitor and assess ancient and recent morphological modifications due to human interventions and their impact on geomorphological processes.
As a consequence of these changes in such urban areas, a progressive increase in geohydrological risk with direct and indirect consequences for people is found, evidencing the crucial requirement to provide adequate and useful management indicators for land planners. Therefore, the study of the constraints and values of urban geomorphological evolution represents an urgent need and a challenge for our modern society. Finally, it should also be noted that the geoheritage of the city needs to be preserved, managed, and where appropriate, enhanced as a possible resource to promote tourism and geotourism as well as leisure activities.