2.1. Study Area: The East Naples Peri-Urban Fringe
The peri-urban space appears as the dominant urban form and challenge of contemporary socio-spatial planning [
14]. The focus on these areas is due to different levels of complexity transited by other disciplines and knowledge that have fertilised and flanked the urban question with the environmental question, landscape integrity and ecological relations. Moreover, these areas represent landscapes in transition aimed at consolidating urban characteristics at the expense of agro-environmental values.
There are many definitions associated with the peri-urban context. The common characteristic of the many different types of space that are considered peri-urban is that they are transitional spaces with a certain degree of mixing of urban and rural uses, resulting in a varied nature of the territory [
15]. This degree of mixture is conditioned by the many overlapping and constantly changing variables (character, structure, thickness, prevalence of land use, way of occupying the space, environmental processes), by the degree of belonging to the two reference sets (urban and rural), by the levels of gravitation (dependence/attraction) with respect to one or more centres, and by belonging to more or less structured metropolitan systems [
16].
Nevertheless, there is a particularly strong difference between the peri-urban areas of developing countries and those of the developed nations of Europe. The former are characterised by poverty, environmental degradation and informal settlements; the latter, to which this study refers, are characterised by low levels of mobility, economic performance, landscape integrity and environmental quality [
17].
This second typology of peri-urban areas hoghlights the result of multipolar organisation particularly evident in large metropolitan areas where the residual space is set as a frontier for greater competitiveness to the urban area that no longer holds a single centre [
18]. They are the product of processes of regionalisation of the urban in which these new urbanisation strategies determine an extended spatial configuration in which not everything is urban but everything is urban-driven [
19]. In pockets of what used to be considered the countryside, a disjointed, additive, stratified and light patchwork extends: a "constitutive outside" [
20] influenced by successive structural adjustment programmes, land expropriations, agro-industrial consolidation and ecological plunder [
19]. These are processes of spoiling that accumulate: first the resources (agrarian, environmental and social), then the expropriation of the capacity to reproduce them to make way for service infrastructures [
21].
This ‘third territory’ of difficult delimitation is placed halfway between urbanity and rurality [
22] plays the role of a ‘bridge-space’ between density and rarefaction [
23] and varies in size and nature according to the increase in urban pressures [
24]. An indeterminated space, no longer to be considered non-urban, linked to dissipative logics or functional decentralisation of informality and waste of urban functioning.
The degradation of prime agricultural land, the deprivation of soil from tree density and water pollution in peri-urban areas are results of a rapid urbanisation that should be re-read within the concept of ecological footprint [
25] or planetary boundaries [
26], aiming at recovering missed opportunities with respect to food self-sufficiency, shortening of supply chains, re-cycling of materials, soil consumption and ecological connections of biodiversity corridors. The implications, therefore, call for ‘re-evaluating people-environment relationships’ rather than focussing on resource extraction or land transitions.
The study area of the East Naples peri-urban fringe represents an urban-rural patchwork of mixed land uses in which a no longer functional agricultural matrix is still legible. Administrative boundaries, spaces and demarcations are no longer discrete, distinct and universal. It is an edge that develops at the fringe of the urban belt of the first ring consolidated around the cores of the historic city. It presents different functions and densities and behaves as a transitional area in which the landscape is characterised by mobility infrastructure and its interstitial spaces, plates of residential construction, low-density settlements, planned and unplanned, old rural cores interspersed with disused or declining production plates [
9]. As the place where the urban expansion process unfolds, heterogeneous expectations and interests make urban planning processes complex. The controversies are amplified by the need to frame these processes in the paradigma of sustainable development. The agricultural palimpsest and the collective domain of related benefits (ecosystem, landscape, food, economic services) are replaced by the accumulation and addition of uses necessary only for urban functioning, through the strategic location of higher functions (landfills, shopping centres, logistics), or in the replication of unplanned settlements.
The two case studies concern two experiences carried out in the Naples Metropolitan Area: the Urban Plan of the municipality of Casoria and the Urban Recovery Programme of the Ponticelli neighbourhood in Naples; they differ in terms of project scale, type of urban planning instrument and purpose of the plan-programme (
Figure 1). The differences also concern the variability of the peri-urban context. This helps to clarify the results of the evaluation model, its implementations and applications.
The peri-urban landscape of Casoria is characterised by a widespread eco-systemic, particle and topological fragmentation and a high density of mobility infrastructure and is subject to continuous pressure from unplanned settlements or expansions for production or logistics or dislocation in which traditional agricultural management is put into crisis. Marginal agricultural areas are contrasted by numerous open spaces with dynamics of under-use and abandonment.
In Ponticelli the condition of peri-urbanity is given by an edge condition between a dense urban system and the conurbation system of the coastal strip of the Metropolitan City of Naples, made up of interstices, residual agricultural uses and large open spaces of public property uncultivated and waiting. The great residential plaques of public housing policies have operated by leaving voids delimited by the infrastructural system, but still potentially linked to a legible agricultural matrix. Spaces with strong infrastructural and political pressures, but also uncertain spaces left unrealised by the public housing policies that built this part of the city, agricultural residues and numerous public properties.
2.1.1 The Municipal Urban Plan of Casoria
The municipality of Casoria is part of the first ring of municipalities that make up the Neapolitan urban fringe that stretches north and east of Naples.
The urban planning tool on which the evaluation model is tested is the Municipal Urban Plan (MUP). This general urban planning tool is prepared by the municipal administration to outline strategic development choices, define public space management policies, identify structuring elements and territorial invariants, and protect the physical and environmental integrity of the territory by enhancing existing resources and their economic and social development. The choices made with these tools guarantee environmental quality and sustainability.
The guidelines dictated by the MUP, which are general in nature and of indefinite duration, are concretely implemented by operational planning. The Programmatic Operational Plan (POP) envisaged by the MUP concerns the rural-periurban territorial unit characterised by the prevalence of rural territories with eco-systemic value, by conditions of particle and topological fragmentation, low settlement density, phenomena of under-utilisation and abandonment, and the crossing of large network infrastructures. The MUP promotes: the use of non-urbanised peri-urban contexts for social purposes, ecological reconnection and environmental rebalancing, foreseeing: the creation of public parks and public use with different naturalistic typologies; the possibility of enhancing agricultural production, also for social, educational and training purposes; the increase in the supply of social and public housing, with zero soil consumption.
The POP implements the provisions of the MUP through the definition of a vast periurban park. This park, covering approximately three square kilometres (a quarter of the entire municipality), is included in the metropolitan ecological network and is aimed at the restoration of ecological continuity, the enhancement of agricultural use, the civic use of public areas, and new community densities. In particular, the POP foresees the creation of social settlements in the park, the construction of a sustainable road network, which connects the area with the urbanised context (road-park, bicycle path and equipped pedestrian path). A further provision is the identification of Minimum Project Units (MPU) in which three levels of land use are identified: equipped green, productive green/productive forest and mitigation green. The latter extends on the edges of MPUs and beyond, i.e. in the public interstitial areas of infrastructures.
2.1.2 The Urban Recovery Programme of the Ponticelli Neighbourhood in Naples
Ponticelli is a district on the eastern outskirts of the municipality of Naples. The urban evolution of the neighbourhood is linked to national public housing policies and to the contingency and acceleration measures that arose in response to natural disasters or as a response to the high housing tension and social hardship in the suburbs.
The urban planning instrument on which the evaluation model is tested is the Urban Recovery Programme (URP). It is a programme with the status of an implementing urban plan and its approval and public financing has the following basic requirements building and urban redevelopment of public housing settlements, also in accordance with the urban planning instruments in force; a systematic set of interventions organised on the basis of a unitary proposal, with different types of intervention (redevelopment, new construction) and the integrative character of the functions (residential, public housing services and production of goods and services); co-participation of public and private implementers and the related economic and organisational resources, with a minimum threshold of 25% private financing for ensuring the public financing of the project.
The Ponticelli URP is designed to rethink the parts left unfinished by the rational design imposed by previous public housing programmes; in fact, already in the 1950s, the first public housing estates were grafted onto Ponticelli as an expansion of the historic centre of the city. The URP reinterprets the design of the suburbs in a contemporary key, confronting it with the rigid constraining system of the volcanic risk of Vesuvius, which in some very dangerous areas (the so called ‘red zones’) does not provide for residential development, and with the superordinate forecasts of the Sustainable Urban Mobility Plan, which envisages the passage of a Bus Rapid Transit connecting with the city centre. The URP envisages the construction of new social housing, areas of private residential expansion to balance the social mix, numerous public facilities, and a forest running through the central spine.
2.2. Data Sources and Approach
For the comparison of the indicators, the evaluation was processed in a Geographic Information System (GIS) environment on a hexagonal grid with 50x50m spacing.
The use of regular polygons proves to be effective for representing the spatial variousness of the phenomena under investigation and is a suitable method for generalising data, statistical mapping, and spatial evaluations [
27]. Another peculiarity of regular-meshed grids is also inherent in the possibility of combining mapping units into new cells at a more detailed resolution, allowing the cumulative effects of state changes to be studied [
28].
For the assessment of the sustainability of the transformations, the indicators are built on the dual pre/post-plan scenario, which allows for a cognitive picture of the state of the environment and an assessment scenario of the achievement of targets. In fact, the ex-ante scenario is intended as a tool for reconstructing the state of the environment to support decision-making [
29]. It addresses the issue of asset mapping, which indicates the process of documenting the tangible and intangible resources of a community by considering the community as a place with strengths or assets that must be preserved and enhanced, not deficits to be remedied [
30]. It allows the construction of a knowledge project capable of initiating a conscious and creative reflection aimed at overcoming the concepts acquired within the interpretative models of modern thought based on a paradigm of perpetual growth and a linear-reductionist functioning of de-contextualisation and resource extraction. Furthermore, it allows the urban design project to orientate its choices towards forms of sustainability and resilience inscribed within the urgencies of 2030 Agenda and understood not only as the capacity to adapt to the pushes of urban transformation and the degenerative forces of land rent, but above all as the injection of elasticity into urban policies to connect resources, actors, identities and tensions in a non-rigid manner, to reactivate functional chains and to reanimate urban metabolisms.
Ex-post evaluation allows the identification of the impacts of transformations by determining the identification of criticality thresholds through the recognition of context limits and by integrating the multidimensional aspects necessary to look at open and multifunctional margins in which different forms of life interact and develop social-ness. The objectives of using multidimensional criteria and specific indicators are different from the mapping and evaluation of context attributes and values in ex-ante evaluations, as ex-post evaluation focuses on the actual impacts generated [
31]. In particular, ex-post evaluation is used to verify that established objectives have been achieved, to determine whether there are unintended or unintended consequences and to evaluate the effectiveness of alternative approaches in the meantime [
31,
32].
The place-based approach makes it possible to support researchers and practitioners addressing complex multidimensional issues with methodologies that can be replicated and implemented to the relevant case study variables. This approach is focused on addressing a problem on a local scale, meeting the needs of a particular context by tapping into local communities and resources [
33,
34] and enabling work on a non-abstract concept of sustainability. They support the theoretical and practical framework taking into account the unique characteristics of a given complex socio-ecological system by aiming to generate locally relevant knowledge and context-specific solutions to address sustainability problems [
35,
36].
2.3. First Phase: Identification of Evaluation Indicators
Sustainability cannot be measured directly [
37] but through a process of implemetation that takes into account the transversality of the concept (economic development, social equity and ecological integrity) [
38] and through metrics or indicators [
39] as a composite of several directly measurable variables that enable the quantification of such multidimensional and complex phenomena [
37,
40].
Indicators and indices, which are born from values (we measure what we care about) and create values (we care about what we measure) [
41], assume instrumental value not only with respect to the type of territory (place-based approach) but above all with respect to the type of urban planning instrument we are evaluating. Their main characteristic is their ability to summarise, focus and condense the enormous complexity of our dynamic environment into a manageable amount of meaningful information [
42]. Furthermore, ‘composite indicators’ can be easier to interpret than trying to find a trend in many separate variables [
43,
44]. Therefore, in order to visualise phenomena, highlight trends, simplify, quantify, analyse and communicate the otherwise complex and complicated information related to sustainability, it is necessary to identify coherence between the goals and targets of the 2030 Agenda and the possibility of the urban plan to have an impact. This coherence gives rise to a relationship of direct or indirect dependence that helps the spatial dimension of the spatial assessment to select the most significant indicators for the peri-urban for the integration of the three dimensions and the explicit rendering of impacts.
The SDGs through which the urban planning project in the peri-urban area was proven to correspond to the sustainability assessment are the numbers: 2, 8, 12, 11, 15 17. The targets of the SDGs were then analysed, and indicators were identified (
Table 1). The indicators of the 2030 Agenda were not always spatialisable, so in some cases an adaptation was developed to express the theme of sustainability. The indicators that fully correspond to the global indicators proposed by the Agenda are: illegal building rate, forest area index, soil sealing, fragmentation of natural and agricultural territory.
2.4. Second Phase: Spatial Sustainability Assessment
All the assessments have been done using the Spatial Sustainability Assessment Model (SSAM) [
45,
46], developed by the Regional Environmental Protection Agency of Umbria and the Environmental Laboratory, a research group within the Applied Economy Unit of the Department of Agricultural, Food and Environmental Sciences (DSA3) of the University of Perugia (Italy). The SSAM model is specifically developed for integrated spatial multi-criteria analysis and combines Multiple-Criteria Decision Analysis (MCDA) with Geographic Information System (GIS), analysing each sustainability dimension by means of the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) process and returning a global sustainability index by means of a weighted summation. The use of the geo-TOPSIS algorithm has already been successfully tested in other spatial classification contexts [
47,
48], as has the integration of GIS and multi-criteria evaluation systems and methods.
MCDAs are part of Decision Support Systems (DSSs); in their most general formulation, they can be considered as a set of systematic procedures that serve to generate, evaluate and select alternative decisions on the basis of convergent criteria, which cannot be commensurate in a traditional way and allow the combination of individual criteria into an overall assessment [
49]. The multidimensionality of decision-making criteria, which must be taken into account in sustainability assessments, can be optimally handled by multi-criteria procedures, through the peculiar introduction of different weighting systems, which vary according to the objectives and structure of the decision problem, and which basically serve to determine priorities of choice or action at various levels of complexity even in multidisciplinary approaches [
50].
GIS enables the construction of an interpretative-knowledge framework of reality through spatial analysis models. It is part of Geographic Information Science (GISci), which is the information science oriented towards the collection, modelling, management, visualization and interpretation of geographic information, consolidated in the reflections on spatial dynamics and the need to read relationships and place measurable and shareable in-formation in space [
51]. Being an integrative disciplinary field, it combines multidisciplinary concepts, theories and techniques, enabling innovative synergies for a greater understanding of territories [
52]. In particular, QGIS, an open-source software flexible to experimental implementations of academic research through the integration of specific plug-ins or tools, was used for the entire project.
The TOPSIS method belongs to MCDA [
53,
54,
55] and uses as a basic concept that the preferred option should have (in Euclidean space) the ‘shortest distance’ to the ‘ideal solution’ and the ‘greatest distance’ to the ‘non-ideal solution’. The Euclidean distance criterion was then used to assess the relative closeness of the of-factors to the final solution, and the final order of option preferences is obtained by con-fronting these relative distances [
56]. This method is particularly useful for research as it can be used to verify the achievement of the 2030 Agenda targets.
MCDAs integrated with GIS enable the development of Spatial Decision Support Systems (SDSS) by combining geographical data with contextual statistical measures analysed by means of preferences and value judgements. This allows both effective communication of assessment results to planners and decision-makers, and the construction of spatial assessments necessary to understand the impacts of urban planning on the territory.
In SSAM, the MCDA model is activated within the GIS software and therefore uses the same interface and database. The interface of the SSAM provides a series of successive screens, in which the user is guided through the initial data input, and subsequently through the execution of the multi-criteria analysis [
45]. The final product of the processing is represented by numerical and tabular outputs, as well as graphical and cartographical outputs. These outputs represent the indices of environmental (
EnvIdeal), eco-nomic (
EcoIdeal) and social (
SocIdeal) sustainability. The indicators of each dimension are agregated by applying TOPSIS, while the different dimensions are then aggregated by using the weighted summation to derive the overall sustainability index (
SustIdeal) [
46]. Furthermore, in addition to the separate calculation of the economic, environmental and social indices, SSAM presents a procedure that can retrace the steps that led to the final result, revealing which indicators and/or procedural steps had the greatest influence on the results obtained [45, 46].