Received: 29 April 2020 Revised: 3 October 2020 Accepted: 13 October 2020 DOI: 10.1002/psp.2402 RESEARCH ARTICLE Polycentric development and local fertility in metropolitan regions: An empirical analysis for Barcelona, Spain Antonio López-Gay1 | Luca Salvati2 1 Department of Geography, Universitat Autònoma de Barcelona & Centre d’Estudis Abstract Demogràfics, Facultat de Lletres, Campus The present study verifies if spatial variability in local fertility reflects the shift from a UAB, Barcelona, Spain 2 monocentric dense settlement model towards a polycentric metropolis organised in Department of Economics and Law, University of Macerata, Macerata, Italy central cores and subcentral locations. The spatial distribution of a crude birth rate in Barcelona's province was investigated for a long time span (1975–2018), identifying Correspondence Luca Salvati, Department of Economics and distinctive trends within five concentric rings around Barcelona at four subperiods Law, University of Macerata, Macerata, Italy. (1975–1985, 1986–1996, 1997–2007 and 2008–2018). Using multivariate explor- Email: luca.salvati@unimc.it atory statistics, local fertility rates were correlated with background indicators delin- eating the socio-economic profile of each municipality in the study area. Fertility rates decreased with the distance from downward Barcelona and with population density. In the first time interval (1975–1985), fertility levels—higher in subcentral municipalities and peri-urban locations than in downtown Barcelona—were positively associated with urban growth. In the following two subperiods (1986–1996 and 1997–2007), the contribution of local fertility to urban growth decreased signifi- cantly, reaching the lowest-low figures at the end of the 1980s. In the most recent time interval (2008–2018), a moderate (and spatially heterogeneous) recovery of fertility rates was observed in subcentral locations. Demographic processes underlying Barcelona's expansion provide evidence in favour of a positive relationship between polycentric development and local fertility. Our article finally debates on the use of fertility indicators in the assessment of monocentric versus polycentric (metropolitan) growth in advanced economies. KEYWORDS demographic indicators, multivariate analysis, residential mobility, Spain, urban sprawl 1 | I N T RO DU CT I O N and disadvantaged neighbourhoods (Gilli, 2009; Meijers, 2008; Musterd & van Zelm, 2001). However, although sprawl is frequently Polycentric development is a common growth path in associated with negative socio-economic and environmental conse- contemporary metropolitan regions (Burger & Meijers, 2012; quences, polycentrism combines the advantages of agglomeration Fernández-Maldonado, Romein, Verkoren, & Parente Paula economies typical of compact cities and the reduced congestion of Pessoa, 2014; Salvati, Ciommi, Serra, & Chelli, 2019). Recent decentralised morphologies (Couch, Petschel-held, & Leontidou, 2007; urbanisation has progressively moved away from traditional Muñiz & Garcia-Lopez, 2010; Oueslati, Alvanides, & Garrod, 2015). In monocentric models shifting towards polycentric agglomerations this regard, polycentric development became a ‘hegemonic’ concept (Parr, 2004; You & Yang, 2017; Zhang & Su, 2016). These transforma- reflecting a more cohesive and spatially balanced growth tions have exerted a strong impact on metropolitan structures leading (Di Feliciantonio & Salvati, 2015; Roca Cladera, Marmolejo Duarte, & to settlement dispersion and socio-economic polarisation in affluent Moix, 2009; Vasanen, 2012). Popul Space Place. 2021;27:e2402. wileyonlinelibrary.com/journal/psp © 2020 John Wiley & Sons, Ltd. 1 of 15 https://doi.org/10.1002/psp.2402 2 of 15 LÓPEZ-GAY AND SALVATI Identification and characterisation of processes and mechanisms progressively less associated with elevation, accessibility and density underlying polycentric development present inherent difficulties gradients (Morelli, Rontos, & Salvati, 2014; Munafò, Salvati, & Zitti, (Garcia-López & Muñiz, 2010, 2011; Pili, Grigoriadis, Carlucci, 2013; Salvati & Carlucci, 2017). In such contexts, a complex interplay Clemente, & Salvati, 2017; Veneri, 2013). Generally speaking, spatial of socio-economic forces influenced fertility rates at different spatial forms, socio-economic structures and the rapidity of their changes scales, from local to regional (e.g., Gavalas, Rontos, & Salvati, 2014; allow discrimination of monocentric and polycentric models (Ciommi, Hank, 2001; Kroll & Kabisch, 2012; Lerch, 2013). Chelli, Carlucci, & Salvati, 2018; Ciommi, Chelli, & Salvati, 2019; De By adopting a multivariate analysis of fertility rates made available Rosa & Salvati, 2016). However, earlier studies have distinguished a at enough detailed spatial domains, our study moves in the debate on sort of ‘hidden polycentrism’ from more subtle and scattered paths of polycentric development and fertility dynamics in Europe, with a urban expansion (Carlucci, Chelli, & Salvati, 2018; Salvati, Guandalini, specific focus on the Mediterranean Region. Analysis of demographic Carlucci, & Chelli, 2017; Colantoni, Grigoriadis, Sateriano, Venanzoni, variables provide a comprehensive view of long-term metropolitan & Salvati, 2016). A long-term investigation of demographic dynamics growth (Lerch, 2019; Muniz, 2009; Salvati, Ciommi, Serra, & in metropolitan regions provides an informative tool to investigate Chelli, 2019), integrating more classical indicators of economic polycentric structures and the related economic functions agglomeration and scale processes. By combining a comprehensive (Champion, 2001). Analysis of the long-term demographic evolution investigation of the spatial variability in fertility rates with a polycen- of residential subcentres—defined as structural elements of a given tric vision of urban growth, our work discusses the local outcome of metropolitan system (Roca Cladera, Marmolejo Duarte, & demographic transitions vis à vis metropolitan change. We hypo- Moix, 2009)—can provide a significant contribution in this direction. thesise that demographic dynamics are spatially asymmetric, being At the same time, assessing the spatial evolution of local fertility at affected by (and in turn influencing) the dominant urban structure different stages of metropolitan development contributes to a refined (Bayona-Carrasco & Gil-Alonso, 2012). In this regard, we intrinsically understanding of urban transitions (e.g., Bocquier & Bree, 2018; verify the contribution of local fertility variations in polycentric Bocquier & Costa, 2015; Boyle, 2003). However, population dynamics development of metropolitan regions, assuming that spatial divides in underlying polycentric development are still poorly investigated in central places, subcentral locations and more peripheral areas have an advanced economies (Burger, de Goei, Van der Laan, & impact on specific demographic behaviours that lead to peculiar Huisman, 2011; Champion, Hugo, & Lattes, 2003; Helbich, 2012). In fertility trends (Kulu, 2013). More specifically, how local contexts this context, a spatially explicit analysis of local fertility rates over a influence fertility levels was investigated in the present study to verify sufficiently long time interval allows a better comprehension of if specific population dynamics have characterised polycentric complex population trends in polycentric regions. development in Barcelona, Spain. Barcelona is one of the oldest cities Considered a reference framework in the analysis of metropolitan in Spain and has taken centuries to evolve into its present state as a regions, polycentrism assumed a normative relevance in the European modern metropolis that has benefited from massive infrastructural Union (Vasanen, 2012), being increasingly intended as a prerequisite growth, immigration from Southern Spain, urban regeneration and for sustainable development (Couch, Petschel-held, & Leontidou, renewal, and spatially asymmetric peri-urban development over the 2007). The Ruhr Basin in Germany, the Randstad in the Netherlands, past decades (Blanco, 2009; Dura-Guimera, 2003; Garcia-Ramon & the Po Valley in Northern Italy and the most urbanised areas of Albet, 2000). The Barcelona's long-term growth is a paradigmatic Belgium are examples of polycentric regions in Europe (Kabisch & example of sequential metropolitan transformations from a Haase, 2011). These regions are organised into an extensive network monocentric and compact structure to polycentrism and spatial of medium–small towns with similar population size and no single scattering (Salvati & Carlucci, 2016). The implications of our work for urban centre, hosting upper economic functions connected with urban management are finally discussed providing policy guidelines smaller centres embedded in a dense infrastructural network for a more cohesive metropolitan growth (Gigliarano & Chelli, 2016). (Parr, 2004). Contrasting the dominant settlement patterns and trends in Western Europe (Salvati & Carlucci, 2016), compact and monocentric 2 | METHODOLOGY urban areas are the most frequent metropolitan form in Southern Europe, representing the most affluent regions in the Mediterranean 2.1 | Study area Basin (Arapoglou & Sayas, 2009; Carlucci, Grigoriadis, Rontos, & Salvati, 2017; Cuadrado-Ciuraneta, Durà-Guimerà, & Salvati, 2017). In Extending 7,726 km2 from the Mediterranean Sea to the Pyrenees this context, demographic transitions have contributed to accelerated (Figure 1), the study area coincides with the administrative borders of urban change, leading to the inherent shift from dense settlements to the Barcelona's province (the third level of European Nomenclature more scattered and spatially discontinuous morphologies (Duvernoy, for Statistical Territorial Units, NUTS) and is partitioned in Zambon, Sateriano, & Salvati, 2018; Gil-Alonso, Bayona-i-Carrasco, & 311 NUTS-5 municipalities. The area has undulated topography Pujadas-i-Rúbies, 2016; Salvati, Sateriano, & Grigoriadis, 2016). consisting of 30% lowlands, 50% uplands and 20% mountains (Salvati Contribution of natural growth and migration to metropolitan growth & Carlucci, 2016). Although urban settlements occupy an important in Southern Europe was particularly heterogeneous over space, being part of the area, most of the region is destined to cropland and LÓPEZ-GAY AND SALVATI 3 of 15 F I G U R E 1 Linear distance of each municipality belonging to the study area from downtown Barcelona (left), subcentral municipalities* (middle), and population density map (inhabitants/km2) at the last census (right). * ‘Subcentres’ include seven towns in Barcelona's metropolitan region (Granollers, Martorell, Matarò, Terrassa, Sabadell, Vilafranca del Penedés and Vilanova i la Geltrù) and three towns in Barcelona's province (Manresa, Vic and Berga); please also refers to Table 2 forests. The study area experienced a massive population increase socio-demographic surveys; results of an empirical analysis of data since the Civil War (Muñiz, Garcia-López, & Galindo, 2008). While collected at that spatial scale are easily interpretable by nontechnical experiencing rapid changes, Barcelona still maintains a wide industrial users such as policymakers and other stakeholders. Finally, although base specialised in metallurgy, chemistry and pharmaceutics spatial planning is coordinated at the national and regional levels in integrated with advanced services and other activities with high value Spain, municipalities take relevant decisions about land destination, added (Dura-Guimera, 2003). Resident population in Barcelona's building volume, settlement size, land taxation and other variables province increased from one million inhabitants (1900) to 5.5 million influencing population distribution and demographic dynamics inhabitants (2010), with a different distribution in core city, subcentral (Sabater & Graham, 2019). A spatially explicit analysis of demographic locations and peri-urban and rural areas (Cuadrado-Ciuraneta, dynamics has further advantages because long-term population data Durà-Guimerà, & Salvati, 2017). For instance, at the beginning of the are freely available from official statistics that can be integrated with 20th century, more than half of total population resided in downtown external data sources and that allow reliable comparisons both across Barcelona, decreasing to 30% in 2010 (Bayona-Carrasco & countries and within regions (Salvati & Serra, 2016). Gil-Alonso, 2012). Peri-urban population expanded more rapidly than For sake of analysis, municipalities in the study area were classi- inner city and rural population all over the study period. Population fied in five concentric rings: (i) the central city coinciding with growth rates during 1900–1950 were higher in downtown Barcelona downtown Barcelona, (ii) 32 municipalities surrounding the core city than in peri-urban municipalities; the reverse pattern was found in the and forming the statutory Barcelona's metropolitan area, subsequent period (1950–2010). Population density increased (iii) 10 subcentral municipalities, (iv) the municipalities forming the progressively in downtown Barcelona until the early 1980s (from 5.4 Barcelona's statutory metropolitan region (except for seven thousand inhabitants/km2 in 1950 to 17.8 thousand inhabitants/km2 subcentres) and (v) the remaining 147 municipalities of the in 1980), decreasing moderately to 16.4 inhabitants/km2 in 2010. A Barcelona's province outside the boundaries of the statutory similar trend was found in subcentral municipalities with a peak metropolitan region (except for three subcentrrs). This spatial struc- density measured in 1980 and a moderate decline afterwards (Salvati ture was originally proposed by Salvati and Carlucci (2016) as an & Carlucci, 2016). Although increasing over time, population density optimal partition for analysis of polycentric urban growth in Barcelona in peri-urban municipalities was lower than the average value province (Figure 1). observed in subcentral locations. 2.3 | Identification of subcentral locations 2.2 | Spatial analysis' unit and territorial structure While being originally based on simplified criteria and variables, for Selection of the spatial analysis' unit is a critical issue in urban studies. example, urban density, identification of subcentral locations has Administrative boundaries identify the most used spatial domains in become increasingly objective and rigorous (Veneri, 2013). Studies regional science. Municipalities have been used largely as the spatial carried out in the 1980s and the 1990s proposed the delimitation of support of basic indicators in regional demography (Couch, subcentres as a result of the joint application of historical, institutional Petschel-held, & Leontidou, 2007; Rontos et al., 2016; Salvati, 2016). and administrative criteria (Muñiz & Garcia-Lopez, 2010). Recent Municipalities are the smallest spatial domain of most economic and studies have used population density, employment density and 4 of 15 LÓPEZ-GAY AND SALVATI building types together to identify subcentres (Fernández-Maldonado, 2.4 | Demographic and contextual variables Romein, Verkoren, & Parente Paula Pessoa, 2014; Garcia-López & Muñiz, 2010; Roca Cladera, Marmolejo Duarte, & Moix, 2009). We A crude fertility rate dividing the number of births over a sufficiently adopted the classification by Salvati and Carlucci (2016) that used long time interval (11 years) by the average number of women in parametric and non-parametric approaches to determine a set of ref- fertile age (15–49 years old) was calculated for each municipality of erence thresholds (cut-offs) considering absolute population values at the study area. The investigated time period was partitioned into four municipal scale. intervals covering 11 years each (1975–1985, 1986–1996, Seven subcentral municipalities situated within the boundaries of 1997–2007 and 2008–2018). We assumed birth rates computed over Barcelona's metropolitan region (Granollers, Martorell, Matarò, a sufficiently long time interval as an intrinsically stable measure of Terrassa, Sabadell, Vilafranca del Penedès and Vilanova i la Geltrù) local fertility (Muniz, 2009). The total number of births registered in were identified according to the criteria mentioned above. They also each municipality, and the total number of inhabitants by gender, age coincide with subcentral locations identified in Muñiz, Galindo, and and year, were derived from the Spanish Population Register held by Garcia-Lopez (2003) and Muñiz and Garcia-Lopez (2010) on the base the National Institute of Statistics (INE). A total of 20 variables were of population, employment and activity density. These are mainly edge calculated at the same spatial scale from various official sources cities concentrating jobs in specialised services (business services, as (Table 1) with the aim at delineating basic characteristics of the area. well as finance, insurance and real estate services) surrounded by Variables include topographic indicators (elevation, proximity to the residential areas. Three additional subcentres outside the boundaries sea coast), accessibility (road network), agglomeration (population of the metropolitan region (Manresa, Vic and Berga) were also density at the beginning of each time interval), residential mobility identified as the head town of the respective rural areas. (migration balance during each time interval), dummies classifying TABLE 1 List of variables considered in this study Variable Temporal schedule Unit of measure (range) Source Total fertility rate 1975–1985, 1986–1996, 1997–2007, % (0–100) IDESCAT 2008–2018 Population density at the beginning 1975, 1986, 1997, 2008 Inhabitants/km2 (0 to ∞) Resident population of the study interval by municipality (INE) Migratory balance (annual rate of 1975–1985, 1986–1996, 1997–2007, % growth) 2008–2018 Distance from Barcelona km (0 to ∞) Analysis on a municipal map (INE) Distance from Granollers Distance from Martorell Distance from Matarò Distance from Terrassa Distance from Sabadell Distance from Vilafrance del Penedés Distance from Vilanonova i la Geltrù Distance from Manresa Distance from Vic Distance from Berga Proximity to the sea coast Coastal municipality (1), otherwise (0) Road accessibility Municipality with a motorway (1), otherwise (0) Elevation km (0 to ∞) Central city, downtown Barcelona Dummy Metropolitan area Subcentres Other municipalities, metropolitan region LÓPEZ-GAY AND SALVATI 5 of 15 municipalities in four groups based on their location (downtown time in the global Moran's coefficients at different bandwidths Barcelona, the metropolitan area, subcentral locations and the provide a comparative estimation of intensity and extent of spatial remaining part of the metropolitan region) and linear distances from interactions between the selected analysis' domains (Salvati & 11 locations (inner city and 10 subcentres). Analysis of distances from Carlucci, 2017). fixed locations identifies the spatial extent of influence for both inner Assuming that local fertility has reflected, especially in specific city and subcentres (Salvati & Carlucci, 2016). time intervals, the urban–rural gap typical of monocentric regions (e.g., Vitali & Billari, 2017), intensity and statistical significance of spatial dependency in total fertility rate at each municipality and time 2.5 | Data analysis interval were respectively assessed over time using local Moran's coefficient of spatial autocorrelation (z-scores) and the related p levels A data mining approach incorporating descriptive statistics, non- at six bandwidths (see above) reflecting a broad range of spatial parametric inference and multivariate exploratory analysis was interactions, from local (10 km) to regional (100 km). By revealing developed in the present study (Serra, Vera, Tulla, & Salvati, 2014). specific spatial regimes that change (more or less rapidly) over time Average local fertility rates were evaluated at five rings for four (Serra, Vera, Tulla, & Salvati, 2014), local Moran's coefficients of consecutive time intervals (1975–1985, 1986–1996, 1997–2007 and spatial autocorrelation allow a diachronic investigation of municipal 2008–2018). Assuming mean rate and spatial variability as the most clusters with different fertility trends illustrated through maps. Based representative measures of a regional demographic process on significant (p < 0.05) local Moran's coefficients at each location, (Muniz, 2009), the relationship between average and coefficient of municipalities were classified in four average spatial regimes as variation in local birth rates was evaluated by year over the entire follows: (i) high–high (HH) hotspots (displaying a trend towards study period with the aim at identifying regime shifts in local fertility. high fertility with similar neighbours), (ii) high–low (HL) clusters (high The spatial distribution of local fertility rates was also illustrated fertility with different neighbours), (iii) low–high (LH) clusters through maps. (low fertility with different neighbours) and (iv) low–low (LL) cold spots (low fertility with similar neighbours). 2.6 | Evaluating the spatial structure of fertility rates 2.7 | The role of local contexts By using global and local Moran's indexes computed for the same A non-parametric Spearman correlation analysis was run to assess the bandwidth ramp, a diachronic analysis of spatial autocorrelation of pairwise relationship between birth rates and each territorial indicator local fertility rates was run separately for each time interval with the described above. Significance of pairwise correlations was tested at aim at (i) verifying spatial homogeneity (or diversification) of p < 0.05 after Bonferroni's correction for multiple comparisons. demographic behaviours over time (global Moran's coefficients) at the Results of this analysis allow identification of background indicators regional scale and (ii) evidencing clusters/spatial outliers (local Moran's with a (linear or non-linear) relationship with local fertility. A multiway coefficients) at the local scale (Cuadrado-Ciuraneta, Durà-Guimerà, & factor analysis (MFA) was run on a data matrix with a structure Salvati, 2017; Pili, Grigoriadis, Carlucci, Clemente, & Salvati, 2017; replicated for four time intervals that incorporates fertility rates and Salvati & Serra, 2016). Persistence (or change over time) in spatial background indicators (see Table 1) at each municipality in the study regimes of fertility may indicate latent (or substantial) transformations in area. MFA is a generalisation of principal component analysis that the regional socio-economic structure, outlining a more or less rapid tran- allows identification of the multivariate relationship between sition to new metropolitan structures (Morelli, Rontos, & Salvati, 2014). background indicators and demographic variables and characterisation A global Moran's index of spatial autocorrelation in total fertility of the most relevant system's changes over time (Salvati & rate was calculated separately for 1975–1985, 1986–1996, Serra, 2016). By selecting factors with eigenvalue >1, MFA 1997–2007 and 2008–2018 considering six bandwidths (10, 20, decomposes the intrinsic dimensions of metropolitan expansion 30, 50, 75 and 100) representative of spatial scales spanning from (e.g., agglomeration and scale) into few relevant, independent factors local (10 km) to regional (100 km). This bandwidth's ramp was adopted quantifying correlation with local fertility and other demographic in earlier studies dealing with socio-demographic processes in Medi- variables (population density and migration balance) at the same time. terranean countries (Salvati, Ciommi, Serra, & Chelli, 2019) with the aim at testing the significance of spatial autocorrelation at urban (10 and 20 km), metropolitan (30 and 50 km) or regional (75 and 3 | RE SU LT S 100 km) scale (Salvati, Sateriano, & Grigoriadis, 2016). By analysing together feature locations and feature values (Zambon, Serra, Sauri, 3.1 | Fertility dynamics in Barcelona Carlucci, & Salvati, 2017), global Moran's coefficients (computed as z-scores) were tested for significance at p < 0.01 under the null Total fertility rate in Barcelona province showed a slightly different hypothesis of no spatial relationship in fertility rates. Changes over trend over time compared with what was observed on a country scale 6 of 15 LÓPEZ-GAY AND SALVATI FIGURE 2 (a) Total fertility rate in Barcelona province by district and (b) comparison with Spanish fertility by year, 1975–2018 in Spain (Figure 2). Fertility in Spain was systematically higher than the rest of Spain. Spatial variability in fertility levels was relatively what was observed in the province of Barcelona until the mid-1990s, modest in the late 1970s and increased in the 1980s and the 1990s, when it reached its lowest low. In Spain, the lowest-low fertility was despite a more intense fertility decline. The highest variability in fertil- observed a few years later, in 1998. Subsequently, the fertility rate ity rate within the study area has been observed since the late 1990s, was systematically higher in Barcelona than in the rest of Spain. A despite the differential trend in total fertility (increasing between continuous recovery in the fertility rate was observed from the late 1997 and 2007, decreasing between 2008 and 2018). Considering 1990s to 2008. The fertility rate decreased slowly in the following fertility rates for homogeneous time intervals, it was observed that decade, narrowing the gap between the province of Barcelona and downtown Barcelona is the area with the lowest fertility for the whole LÓPEZ-GAY AND SALVATI 7 of 15 TABLE 2 Total fertility rate by time interval and district in Barcelona, 1975–2018 District 1975–1985 1986–1996 1997–2007 2008–2018 a Downtown Barcelona 1.93 1.16 1.29 1.29 Barcelona metropolitan areab 2.21 1.21 1.42 1.46 c Subcentres 2.25 1.37 1.59 1.59 Barcelona metropolitan regiond 2.11 1.39 1.60 1.44 e Barcelona province 1.97 1.32 1.51 1.55 a b The central municipality of Barcelona. Thirty-two municipalities belonging to the administrative area of metropolitan Barcelona excluding the central municipality of Barcelona. cTen subcentral municipalities in Barcelona province. dThe remaining municipalities of the metropolitan region of Barcelona (excluding the central municipality of Barcelona and seven subcentral municipalities located in the region). eThe remaining municipalities of Barcelona province (excluding three subcentral municipalities located outside the metropolitan region of Barcelona. period considered (Table 2). The rural area outside the Barcelona fertility distributed more homogeneously across space. Spatial analysis metropolitan region showed low fertility rates until the mid-1990s, identified a central belt, which includes the municipality of Barcelona recovering quite rapidly in the subsequent period. The first peripheral and the neighbouring municipalities belonging to the metropolitan crown of Barcelona (metropolitan area) showed high fertility in the area, from a more peripheral belt, which includes rural and mountain first time interval, followed by a rapid fertility reduction in the municipalities in the Pyrenees region. An intermediate zone with high following period. Subcentral municipalities had the highest fertility fertility (corresponding to suburban municipalities) separated these rates in the first and fourth time frames. The remaining municipalities two areas. Subcentral municipalities had the highest level of total fer- in the metropolitan region had high fertility rates, aligned with those tility. However, a random distribution was observed in the last sub- recorded in subcentral municipalities in the second and third time period, with a clearer distinction between accessible suburban intervals, and significantly lower than those recorded in the subcentral municipalities and marginal areas coinciding with the mountainous municipalities in the first and fourth time intervals. The total fertility region of the Pyrenees. rate was significantly different in the five areas into which the province of Barcelona was divided for all time intervals considered in this study (Kruskal–Wallis H test, p < 0.05). Furthermore, the total 3.2 | Spatial analysis of local fertility rates fertility rate of subcentral municipalities was significantly higher than the total fertility rate of the remaining municipalities in the study area The analysis of the spatial structure of total fertility rate was carried for all time intervals (Mann–Whitney U test, p < 0.05). This evidence out using Moran's global and local spatial autocorrelation indices. suggests that fertility rates in Barcelona followed a typical urban– Table 3 reports the global Moran index separately for the four study suburban–rural gradient. On average, subcentres had the highest periods. In the first period, the spatial correlation was significant on a fertility in the study area. local scale (bandwidths between 10 and 30 km), being not significant Figure 3 illustrates the relationship between the average level of on a larger scale (bandwidths greater than 30 km). In the second fertility at the regional scale and the spatial variability of fertility at period, the spatial distribution of the fertility rate proved to be ran- the local scale distinguishing among time intervals. Two indicators dom: a significant Moran's coefficient was only observed for the were analysed, both of which showed a homogeneous pattern in the 20-km bandwidth. In the third period, the Moran's coefficients were first two decades and more heterogeneous patterns in the following significant for all bandwidths, suggesting a highly clustered spatial years. Althouhg constant variability across areas and a slow (but structure on both urban and metropolitan scale. The same evidence continuous) fertility reduction on a regional scale were observed until was collected for the last period, with the only exception of the the first half of the 1990s, the specific trend observed in the following 10-km bandwidth. period suggests a greater unpredictability of regional demographic Figure 5 illustrates the study area municipalities classified on the patterns. These became progressively more heterogeneous over time basis of the prevailing spatial pattern according to the local Moran's and space, both in a context of slow fertility recovery (1997–2007) coefficient. Being in line with the results of the global Moran's index, and under a new, and more intense, decline in local fertility the municipalities classified with a specific and significant spatial pat- (2008–2018). tern (HH, LL, HL or LH) in the first two periods are very few and have The spatial distribution of total fertility rate was illustrated in a random spatial distribution. In the second period, the local fertility Figure 4. The reduction of average fertility levels between the first rate showed a more evident spatial heterogeneity in peripheral rural and second time intervals was evident, although the spatial distribu- municipalities belonging to the mountainous region of the Pyrenees. tion of birth rates was rather heterogeneous in both cases. Fertility A predominance of municipalities with HH (high fertility hotspots on a levels were particularly high in some municipalities, while not directly local scale) in the suburban belt was observed in the third period. Sub- associated with any geographical gradient. In the third subperiod, local central municipalities and the surrounding municipalities were 8 of 15 LÓPEZ-GAY AND SALVATI F I G U R E 3 Relationship between (a) average and coefficient of variation of total fertility rates, municipal-scale and between (b) median and average-to-median total fertility rate, municipal-scale (right) in Barcelona province (left) by year (1975–2018) classified at this spatial pattern. The reverse trend has been observed study period, total fertility rate was significantly higher in coastal in the mountainous area, where the municipalities classified as cold- municipalities and in locations within the metropolitan area of spot (LL) predominate, indicating a homogeneously low fertility rate. Barcelona. In the second period, fertility levels increased with a The fourth period was finally characterised by a substantial homoge- positive migration balance and with the distance from Berga. More neity of local fertility in the most accessible locations (urban and generally, the highest fertility has been observed in suburban munici- suburban), a low fertility cold-spot consolidated in peripheral areas. palities of the metropolitan region of Barcelona. In the third period, fertility decreased with elevation, the distance from Barcelona and from all subcentres of the metropolitan region, while increasing with 3.3 | Analysis of the local context the distance from Berga, population density, migration balance and accessibility. In the fourth period, fertility levels decreased with eleva- The impact of local contexts on total fertility rates was tested using tion and the distance from five subcentres (Martorell, Terrassa, Spearman's non-parametric correlation analysis (Table 4). In the first Sabadell, Vilafranca del Penedès and Vilanova i la Geltrù) and LÓPEZ-GAY AND SALVATI 9 of 15 F I G U R E 4 Spatial distribution of total fertility rate in Barcelona province by time interval: 1975–1985 (upper left), 1986–1996 (upper right), 1997–2007 (lower left) and 2008–2018 (lower right) T A B L E 3 Global Moran's spatial autocorrelation index of total fertility rate in Barcelona's province, 1975–2018, by time interval and bandwidth (km); I = Moran's index; z = z-score of Moran's index; p = probability level of Moran's index 1975–1985 1986–1996 1997–2007 2008–2018 Band I z p I z p I z p I z p 10 0.082 2.68 0.007 0.041 1.38 0.167 0.187 5.97 0.000 0.076 2.50 0.012 20 0.040 2.49 0.000 0.022 2.80 0.005 0.193 11.26 0.000 0.063 3.79 0.000 30 0.032 2.80 0.005 0.023 2.04 0.041 0.178 14.46 0.000 0.055 4.64 0.000 50 0.014 2.12 0.034 0.011 1.77 0.076 0.141 17.49 0.000 0.034 4.49 0.000 75 0.009 2.09 0.037 0.012 2.55 0.011 0.109 18.37 0.000 0.027 5.03 0.000 100 0.008 2.25 0.025 0.008 2.23 0.026 0.089 17.85 0.000 0.023 5.11 0.000 10 of 15 LÓPEZ-GAY AND SALVATI increased with population density and migration balance. The local variance, whereas the second and third axes explained 22.7% and Moran's spatial autocorrelation index of total fertility rate showed no 12.0% of the total variance, respectively. The first axis illustrates the significant correlation with any contextual variable in the first and urban concentration gradient in Barcelona. Population density was fourth periods, being significantly higher in Barcelona metropolitan significantly associated with Axis 1 for all study periods, with loadings area in the second period. In the third period, the Moran's index systematically higher than 0.9 and increasing over time. Migration bal- increased with elevation and decreased with population density. ance was positively associated with Axis 2, displaying intermediate These results indicate that low fertility rates concentrated in less coefficients in the first and fourth periods and very high coefficients accessible mountainous municipalities. in the second and third periods. The total fertility rate was associated The diachronic analysis of the multivariate relationship between negatively with Axis 3 in the first and second period, resulting instead demographic variables and contextual indicators (Table 5) extracted positively associated with Axis 2 in the third period. Axis 1 was nega- three significant axes with eigenvalue >1 and cumulated variance tively correlated with elevation and the distances from Barcelona and above 71%. In particular, the first axis explained 36.4% of the total five subcentres and positively correlated with the distance from F I G U R E 5 Spatial distribution of the local Moran's z-score of spatial autocorrelation of total fertility rate in Barcelona province by time interval: 1975–1985 (upper left), 1986–1996 (upper right), 1997–2007 (lower left) and 2008–2018 (lower right)*. * ‘HH’ and ‘LL’ respectively indicate a ‘high–high’ hotspot or a ‘low–low’ cold-spot; ‘HL’ and ‘LH’ respectively indicate ‘high–low’ and ‘low–high’ clusters LÓPEZ-GAY AND SALVATI 11 of 15 T A B L E 4 Non-parametric Spearman pairwise correlation coefficients between selected territorial variables and (i) total fertility rate or (ii) local Moran's standardised coefficients of spatial autocorrelation in total fertility rate, Barcelona province, 1975–2018 (only significant coefficients at p < 0.05 after Bonferroni's correction for multiple comparisons were shown) Total fertility rate Local Moran's z-score Variable 1975–1985 1986–1996 1997–2007 2008–2018 1975–1985 1986–1996 1997–2007 2008–2018 Distance from Barcelona −0.38 Granollers −0.29 Martorell −0.38 −0.20 Matarò −0.29 Terrassa −0.34 −0.18 Sabadell −0.35 −0.16 Vilafranca del Penedès −0.33 −0.16 Vilanova i la Geltrù −0.35 −0.16 Manresa Vic Berga 0.17 0.38 Proximity to the sea 0.16 coast Accessibility 0.26 Elevation −0.33 −0.17 0.18 Population density 0.20 0.23 −0.26 Migratory balance 0.42 0.68 0.33 Barcelona metro areaa 0.16 0.16 Subcentresa Rest of Barcelona metro. 0.17 0.39 rea a Dummy variables. Berga. Axis 2 was not correlated with any contextual indicator, relevant issue in the case of large cities expanding for a long time in a whereas Axis 3 was weakly correlated with accessibility. compact fashion (Di Feliciantonio & Salvati, 2015). Population deconcentration and suburbanization represents the most recent urban development path in Mediterranean countries 4 | DISCUSSION (Bayona-Carrasco & Gil-Alonso, 2012). How this path may alter the traditional monocentric form observed in Mediterranean cities As a result of compact urbanisation, population growth, economic res- towards a more polycentric spatial asset is an intriguing question tructuring and class segregation, metropolitan development in Europe (Arapoglou & Sayas, 2009). Use of demographic indicators allows a was increasingly oriented towards polycentric models refined assessment of different morphological and functional dimen- (Vasanen, 2012). In this perspective, the European Spatial Planning sions of urban growth in such contexts (Bocquier & Costa, 2015; Framework has interpreted polycentrism as a target of social cohesion Bradbury, Peterson, & Liu, 2014; Van Nimwegen, 2013). Going and territorial sustainability (Westerink et al., 2013). Reflecting social beyond the lack of long time series of key variables such as employ- homogeneity, dense settlement expansion and urban congestion, ment or building density, our spatially detailed approach benefits from monocentric models in Southern Europe have revealed peculiar form– the extensive use of demographic indicators. These indicators are function relationships (Carlucci, Grigoriadis, Rontos, & Salvati, 2017). based on homogeneous time series derived from vital statistics At the same time, with urban growth being often associated with set- available at a disaggregated spatial scale (Chelli, Gigliarano, & tlement informality and lassez-faire planning (Couch, Petschel-held, & Mattioli, 2009). Leontidou, 2007; Cuadrado-Ciuraneta, Durà-Guimerà, & Salvati, The present study definitely contributes to a refined analysis of 2017; Munafò et al., 2013), polycentrism in Mediterranean Europe fertility dynamics in polycentric regions. The lack of a specific analysis was only partly effective in achieving targets of environmental sus- of fertility trends in central cities, residential subcentres and peri- tainability, social equity, economic competitiveness and spatial cohe- urban and rural areas in Southern Europe justifies the approach for- sion (Chelli, Ciommi, Emili, Gigliarano, & Taralli, 2016). This is a mulated in this study. Assuming that subcentres are the most relevant 12 of 15 LÓPEZ-GAY AND SALVATI T A B L E 5 Loadings of a multiway factor analysis on the first three differentiation in local fertility. Subcentral municipalities have experi- axes by time interval (only significant coefficients were shown) enced rapid transformations reflected into differential fertility levels Variable Axis 1 Axis 2 Axis 3 in respect with neighbouring areas. With the increasing role of sub- Population density centres, Barcelona expansion was progressively oriented towards polycentrism since the 1980s. 1975–1985 0.92 In the last decades, the study area has progressively assumed the 1986–1996 0.95 typical traits of moderately polycentric regions (widespread and spa- 1997–2007 0.97 tially balanced medium-density settlements with a progressive decon- 2008–2018 0.98 centration of the inner city). Population growth in subcentral Migration balance municipalities, already observed between the 1950s and the 1980s, 1975–1985 0.50 continued unaltered in the subsequent decades, slowing down since 1986–1996 0.83 the early 2010s. Although being sometimes criticised, the Barcelona's 1997–2007 0.85 model highlights how inner city deconcentration and endogenous 2008–2018 0.50 development of subcentral locations have resulted in a more balanced Total fertility rate spatial structure. This process was clearly associated with a particu- 1975–1985 −0.76 larly high fertility of local communities living in subcentral locations 1986–1996 −0.56 during the early 2000s. These findings complement and corroborate 1997–2007 0.58 the suburban fertility hypothesis, highlighting a specific role for the socio-economic context typical of subcentral locations. 2008–2018 Kulu and Boyle (2009) observed that fertility levels in Finland Distance from Barcelona −0.71 were the highest in small towns and rural areas and the lowest in the Granollers −0.58 capital city. Although socio-economic characteristics of women and Martorell −0.50 selective migrations account for a small portion of fertility variation Matarò −0.57 across settlements, housing conditions and contextual effects explain Terrassa −0.52 a significant portion of urban–rural fertility variation, especially for the Sabadell −0.63 first birth. In Britain, Kulu and Washbrook (2014) demonstrated that Vilafranca del Penedès (i) fertility levels decline as the size of an urban area increases and that Vilanova i la Geltrù (ii) suburban locations have significantly higher fertility levels than city Manresa centres. Fertility differences by residential context persist when con- Vic trolling for the effect of population composition and selective migra- Berga 0.59 tions. By analysing the cumulative fertility of cohorts whose fertility Proximity to the sea coast was completed before and after the change in political regime in 1989, Vobecká and Piguet (2012) argued that education and residen- Accessibility 0.25 tial context (urban–suburban–rural gradient) exerted important effects Elevation −0.75 on the cohorts with (almost) completed fertility in the Czech Republic. Population density The rapid increase in the number of babies born in suburban areas Migratory balance between 1991 and 2007 was due to the selective residential migra- Barcelona metro. areaa tion of young couples and results not just from the larger cohorts of Subcentresa potential mothers but also from the higher fertility of new resident Rest of Barcelona metro.rea 0.59 0.26 couples owing to their more reproduction-oriented values. Although Explained variance (%) 36.4 22.7 12.0 urban–rural dichotomy in fertility levels is a simplification of complex a Dummy variables. spatial dynamics, these factors are also evident in Barcelona, con- firming the specific contribution of subcentral municipalities to higher suburban fertility rates. engine of polycentric development, our analysis compares fertility Causes of the existence of an intermediate group of municipali- rates in core cities, subcentral locations and the surrounding rural ties (subcentres and surrounding locations) with specific fertility areas over a sufficiently long time interval, evidencing the specific role trends should be better investigated on a regional scale. Diversifica- of endogenous and exogenous population growth and the (changing) tion of marriage and childbearing behaviours shaping fertility levels in local contexts in metropolitan expansion. More specifically, this work neighbouring locations of the same metropolitan area indicate that proposes a model of urban expansion fuelled by spatially asymmetric urban spillover processes, which have shaped Barcelona's expansion demographic behaviours. Considering four distinct time intervals that over the last 30 years, are producing subcentral spaces with mixed reflect divergent demographic patterns at regional and country scale, economic functions and diversified social traits (Cuadrado-Ciuraneta, the analysis carried out on a municipal scale shows a strong Durà-Guimerà, & Salvati, 2017; Dura-Guimera, 2003; Salvati & LÓPEZ-GAY AND SALVATI 13 of 15 Carlucci, 2016). Because immigration accounted (and still accounts) competitiveness, urban containment and sustainable settlement/housing for the largest contribution to population growth in subcentral loca- conditions together, by addressing the specificity of different territorial tions (Bayona-Carrasco & Gil-Alonso, 2012), this process has clearly contexts (e.g., distinguishing subcentral locations from neighbouring contributed to local fertility, especially in earlier decades. peri-urban municipalities). Assuming that top-down policies sometimes The empirical results of our study are also coherent with the out- ignore the complexity of regional dimensions of intervention come of earlier studies (e.g., Roca Cladera, Marmolejo Duarte, & (Meijers, 2008), place-oriented strategies replacing top-down policies Moix, 2009), indicating the ambivalence of a functionally polycentric designed at country and supranational scales seem to be more model with a morphologically monocentric form centred on down- appropriate to face with this policy target (e.g., Chelli, Ciommi, Emili, town Barcelona. While presenting distinctive fertility traits at the local Gigliarano, & Taralli, 2016). In this regard, polycentric development is scale, this ambivalence was reflected sometimes in heterogeneous intended as the result of a broader strategy grounded on participative demographic dynamics at metropolitan scale. These findings suggest processes raising awareness of local communities to spatially balanced that Barcelona's spatial organisation can be interpreted as a mixed mechanisms of regional growth. scattered-polycentric model (Muñiz, Galindo, & Garcia-Lopez, 2003). Although the spatial structure of activities and jobs in the metropoli- tan region of Barcelona definitely suggests a polycentric location 5 | CONC LU SIONS model with distinctive subcentres (Garcia-López & Muñiz, 2011), mor- phological indicators indicate only a moderate development around A spatiotemporal analysis of local fertility rates in a representative these subcentres (Salvati & Carlucci, 2016). The spatial distribution of case of Southern Europe may indicate distinctive development paths subcentres (mostly of them distant less than 30 km from downtown from monocentric to polycentric structures. Fertility rates in subcen- Barcelona) may justify these results. Moreover, the less important role tral locations were the highest in the study area for a long time, of subcentral towns in the rest of Barcelona province (e.g., Berga) indi- indirectly supporting (and fortifying the theoretical assumptions of) rectly confirms our assumption about the ambivalence of the the suburban fertility hypothesis. The novelty of this study lies in Barcelona polycentric-scattered model of urban expansion (Zambon, the use of simplified and generalizable criteria for identification of Serra, Sauri, Carlucci, & Salvati, 2017). demographic dynamics in subcentral locations compared with urban In these regards, our study indicates how diachronic analyses car- and rural areas. By considering structural fertility changes and ried out using local-scale data derived from official statistics are mean- spatial variability over a sufficiently long time span, our analysis ingful when debating about the changing spatial organisation of provides original elements supporting a new interpretation of the metropolitan regions. The empirical results of our study may also long-term expansion of compact cities shifting towards inform policies supporting local fertility in spatially balanced regions polycentrism. Demographic dynamics underlying Barcelona's growth that can be generalised to other socio-economic contexts typical of suggest how the (supposed) heterogeneity in forms and functions of advanced economies. An informative base of indicators assessing the Mediterranean cities is shaped by place-specific development formation and consolidation of subcentres is useful when designing patterns, the spatial organisation of consolidated and new residential alternative development scenarios for large Mediterranean cities settlements and local-scale planning strategies reflecting path- competing with the wealthiest and ‘globalised’ agglomerations of dependent urban morphologies. Western Europe. Results of our study finally demonstrate the importance of interpreting different demographic, economic and CONFLIC T OF INT ER E ST cultural indicators within concrete historical backgrounds (Reher & On behalf of all authors, the corresponding author states that there is Iriso-Napal, 1989; Rodriguez-Rodriguez, 2000; Roig & Castro no conflict of interest. Martín, 2007; Rosti & Chelli, 2009). While suggesting that the partial failure of polycentric development reflects the persistence of place- OR CID specific social traits and an insufficient participation to planning decisions in Mediterranean Europe, our study indicates the urgent Antonio López-Gay https://orcid.org/0000-0001-8892-2816 Luca Salvati https://orcid.org/0000-0003-3567-661X need of strategies promoting a demographic rebalance of central and peripheral areas through specific stimuli for subcentral development and delocalization of high-value-added activities in peri-urban areas. RE FE RE NCE S Arapoglou, V. P., & Sayas, J. (2009). New facets of urban segregation in From a demographic perspective, polycentric development should southern Europe. European Urban and Regional Studies, 16(4), support social conditions (e.g., job and housing) leading to equity, 345–362. cohesion, competitiveness and environmental security (e.g., Chelli & Bayona-Carrasco, J., & Gil-Alonso, F. (2012). Suburbanisation and interna- Rosti, 2002; Maloutas, 2007; Rosti & Chelli, 2012). Place-specific and tional immigration: The case of the Barcelona Metropolitan Region multiscale strategies stimulating local competitiveness and social targets (1998-2009). Tijdschrift voor Economische en Sociale Geographie, 103 (3), 312–329. may identify a new development path oriented towards polycentrism Blanco, I. (2009). Does a 'Barcelona model' really exist? Periods, territories and demographic balance (Lerch, 2016). Our findings contribute to a and actors in the process of urban transformation. Local Government generalised design of more effective policies that promote regional Studies, 35(3), 355–369. 14 of 15 LÓPEZ-GAY AND SALVATI Bocquier, P., & Bree, S. (2018). A regional perspective on the economic Dura-Guimera, A. (2003). Population deconcentration and social determinants of urban transition in 19th-century France. Demographic restructuring in Barcelona, a European Mediterranean city. Cities, 20 Research, 38, 1535–1576. (6), 387–394. Bocquier, P., & Costa, R. (2015). Which transition come first? Urban and Duvernoy, I., Zambon, I., Sateriano, A., & Salvati, L. (2018). Pictures from demographic transitions in Belgium and Sweden. Demographic the other side of the fringe: Urban growth and peri-urban agriculture Research, 33, 1297–1332. in a post-industrial city (Toulouse, France). Journal of Rural Studies, 57, Boyle, P. J. (2003). Population geography: Does geography matter in 25–35. fertility research? Progress in Human Geography, 27(5), 615–626. Fernández-Maldonado, A. M., Romein, A., Verkoren, O., & Parente Paula Bradbury, M., Peterson, M. N., & Liu, J. (2014). Long-term dynamics of Pessoa, R. (2014). Polycentric structures in Latin American metropoli- household size and their environmental implications. Population and tan areas: Identifying employment sub-centres. Regional Studies, 48 Environment, 36(1), 73–84. (12), 1954–1971. Burger, M., & Meijers, E. (2012). Form follows function? Linking Garcia-López, M. A., & Muñiz, I. (2010). Employment decentralisation: morphologica and functional polycentricity. Urban Studies, 49(5), Polycentricity or scatteration? The case of Barcelona. Urban Studies, 1127–1149. 47(14), 3035–3056. Burger, M. J., de Goei, B., Van der Laan, L., & Huisman, F. J. (2011). Garcia-López, M. A., & Muñiz, I. (2011). Urban spatial structure, Heterogeneous development of metropolitan spatial structure: agglomeration economies, and economic growth in Barcelona: An Evidence from commuting patterns in English and Welsh city-regions, intra-metropolitan perspective. Papers in Regional Science, 92(3), 1981–2001. Cities, 28(2), 160–170. 515–534. Carlucci, M., Chelli, F. M., & Salvati, L. (2018). Toward a new cycle: Short- Garcia-Ramon, M. D., & Albet, A. (2000). Pre-Olympic and post-Olympic term population dynamics, gentrification, and re-urbanization of Milan Barcelona, a model for urban regeneration today? Environment and (Italy). Sustainability (Switzerland), 10(9), 3014. Planning a, 32, 1331–1334. Carlucci, M., Grigoriadis, E., Rontos, K., & Salvati, L. (2017). Revisiting an Gavalas, V. S., Rontos, K., & Salvati, L. (2014). Who becomes an unwed hegemonic concept: Long-term 'Mediterranean urbanization' in mother in Greece? Socio-demographic and geographical aspects of an between city re-polarization and metropolitan decline. Applied Spatial emerging phenomenon. Population, Space and Place, 20(3), 250–263. Analysis and Policy, 10(3), 347–362. Gigliarano, C., & Chelli, F. M. (2016). Measuring inter-temporal Champion, A., Hugo, G., & Lattes, A. (2003). Towards a new conceptualiza- intragenerational mobility: An application to the Italian labour market. tion of settlement for demography: Beyond the urban/rural Quality and Quantity, 50(1), 89–102. dichotomy. Population and Development Review, 29, 277–297. Gil-Alonso, F., Bayona-i-Carrasco, J., & Pujadas-i-Rúbies, I. (2016). From Champion, A. G. (2001). A changing demographic regime and evolving boom to crash: Spanish urban areas in a decade of change polycentric urban regions: Consequences for the size, composition (2001–2011). European Urban and Regional Studies, 23(2), 198–216. and distribution of city populations. Urban Studies, 38(4), Gilli, F. (2009). Sprawl or reagglomeration? The dynamics of employment 657–677. deconcentration and industrial transformation in greater Paris. Urban Chelli, F., Gigliarano, C., & Mattioli, E. (2009). The impact of inflation on Studies, 46(7), 1385–1420. heterogeneous groups of households: An application to Italy. Hank, K. (2001). Regional fertility differences in western Germany: An Economics Bulletin, 29(2), 1276–1295. overview of the literature and recent descriptive findings. International Chelli, F., & Rosti, L. (2002). Age and gender differences in Italian workers' Journal of Population Geography, 7(4), 243–257. mobility. International Journal of Manpower, 23(4), 313–325. Helbich, M. (2012). Beyond postsuburbia? Multifunctional service agglom- Chelli, F. M., Ciommi, M., Emili, A., Gigliarano, C., & Taralli, S. (2016). eration in Vienna's urban fringe. Tijdschrift voor Economische en Sociale Assessing the equitable and sustainable well-being of the Italian Geographie, 103(1), 39–52. provinces. International Journal of Uncertainty, Fuzziness and Knowlege- Kabisch, N., & Haase, D. (2011). Diversifying European agglomerations: Based Systems, 24, 39–62. Evidence of urban population trends for the 21st century. Population, Ciommi, M., Chelli, F. M., Carlucci, M., & Salvati, L. (2018). Urban growth Space and Place, 17(3), 236–253. and demographic dynamics in southern Europe: Toward a new Kroll, F., & Kabisch, N. (2012). The relation of diverging urban growth pro- statistical approach to regional science. Sustainability (Switzerland), 10 cesses and demographic change along an urban–rural gradient. Popula- (8), 2765. tion, Space and Place, 18(3), 260–276. Ciommi, M., Chelli, F. M., & Salvati, L. (2019). Integrating parametric and Kulu, H. (2013). Why do fertility levels vary between urban and rural non-parametric multivariate analysis of urban growth and commuting areas? Regional Studies, 47(6), 895–912. patterns in a European metropolitan area. Quality and Quantity, 53(2), Kulu, H., & Boyle, P. J. (2009). High fertility in city suburbs: Compositional 957–979. or contextual effects? European Journal of Population, 25(2), 157–174. Colantoni, A., Grigoriadis, E., Sateriano, A., Venanzoni, G., & Salvati, L. Kulu, H., & Washbrook, E. (2014). Residential context, migration and fertil- (2016). Cities as selective land predators? A lesson on urban growth, ity in a modern urban society. Advances in Life Course Research, 21, deregulated planning and sprawl containment. Science of the Total Envi- 168–182. https://doi.org/10.1016/j.alcr.2014.01.001 ronment, 545, 329–339. Lerch, M. (2013). Fertility decline during Albania's societal crisis and its Couch, C., Petschel-held, G., & Leontidou, L. (2007). Urban sprawl in subsequent consolidation. European Journal of Population, 29(2), Europe: Landscapes, land-use change and policy. London: Blackwell. 195–220. Cuadrado-Ciuraneta, S., Durà-Guimerà, A., & Salvati, L. (2017). Not only Lerch, M. (2016). Internal and international migration across the urban tourism: Unravelling suburbanization, second-home expansion and hierarchy in Albania. Population Research and Policy Review, 35(6), ‘rural’ sprawl in Catalonia, Spain. Urban Geography, 38(1), 66–89. 851–876. https://doi.org/10.1007/s11113-016-9404-2 De Rosa, S., & Salvati, L. (2016). Beyond a ‘side street story’? Naples from Lerch, M. (2019). Regional variations in the rural-urban fertility gradient in spontaneous centrality to entropic polycentricism, towards a ‘crisis the global South. PLoS ONE, 14(7), e0219624. https://doi.org/10. city’. Cities, 51, 74–83. 1371/journal.pone.0219624 Di Feliciantonio, C., & Salvati, L. (2015). ‘Southern’ alternatives of urban Maloutas, T. (2007). Segregation, social polarization and immigration in diffusion: Investigating settlement characteristics and socio-economic Athens during the 1990s: theoretical expectations and contextual patterns in three Mediterranean regions. Tijdschrift voor Economische difference. International Journal of Urban and Regional Research, 31(4), en Sociale Geografie, 106(4), 453–470. 733–758. LÓPEZ-GAY AND SALVATI 15 of 15 Meijers, E. (2008). Measuring polycentricity and its promises. European Salvati, L., & Carlucci, M. (2017). Urban growth, population, and recession: Planning Studies, 16(9), 1313–1323. Unveiling multiple spatial patterns of demographic indicators in a Morelli, V. G., Rontos, K., & Salvati, L. (2014). Between suburbanisation Mediterranean City. Population, Space and Place, 23(8), e2079. and re-urbanisation: revisiting the urban life cycle in a Mediterranean Salvati, L., Ciommi, M. T., Serra, P., & Chelli, F. M. (2019). Exploring the compact city. Urban Research & Practice, 7(1), 74–88. spatial structure of housing prices under economic expansion and Munafò, M., Salvati, L., & Zitti, M. (2013). Estimating soil sealing rate at stagnation: The role of socio-demographic factors in metropolitan national level—Italy as a case study. Ecological Indicators, 26, 137–140. Rome, Italy. Land Use Policy, 81, 143–152. Muñiz, I., Galindo, A., & Garcia-Lopez, M. A. (2003). Cubic spline Salvati, L., Guandalini, A., Carlucci, M., & Chelli, F. M. (2017). An empirical population density functions and satellite cities delimitation: The case assessment of human development through remote sensing: of Barcelona. Urban Studies, 40(7), 1303–1321. Evidences from Italy. Ecological Indicators, 78, 167–172. Muñiz, I., & Garcia-Lopez, M. A. (2010). The polycentric knowledge econ- Salvati, L., Sateriano, A., & Grigoriadis, S. (2016). Crisis and the city: omy in Barcelona. Urban Geography, 31(6), 774–799. Profiling urban growth under economic expansion and stagnation. Muñiz, I., Garcia-López, M. A., & Galindo, A. (2008). The effect of employ- Letters in Spatial and Resource Sciences, 9(3), 329–342. ment sub-centres on population density in Barcelona. Urban Studies, Salvati, L., & Serra, P. (2016). Estimating rapidity of change in complex 45(3), 627–649. urban systems: A multidimensional, local-scale approach. Geographical Muniz, J. O. (2009). Spatial dependence and heterogeneity in ten years of Analysis, 48(2), 132–156. fertility decline in Brazil. Population Review, 48(2), 32–65. Serra, P., Vera, A., Tulla, A. F., & Salvati, L. (2014). Beyond urban–rural Musterd, S., & van Zelm, I. (2001). Polycentricity, households and the dichotomy: Exploring socioeconomic and land-use processes of identity of places. Urban Studies, 38(4), 679–696. change in Spain (1991–2011). Applied Geography, 55, 71–81. Oueslati, W., Alvanides, S., & Garrod, G. (2015). Determinants of urban Van Nimwegen, N. (2013). Population change in Europe: Turning sprawl in European cities. Urban Studies, 52(9), 1594–1614. https:// challenges into opportunities. Genus, 69(1), 103–125. doi.org/10.1177/0042098015577773 Vasanen, A. (2012). Functional polycentricity: Examining metropolitan Parr, J. (2004). The polycentric urban region: A closer inspection. Regional spatial structure through the connectivity of urban sub-centres. Urban Studies, 38(3), 231–240. Studies, 49(16), 3627–3644. Pili, S., Grigoriadis, E., Carlucci, M., Clemente, M., & Salvati, L. (2017). Veneri, P. (2013). The identification of sub-centres in two Italian Towards sustainable growth? A multi-criteria assessment of (changing) metropolitan areas: A functional approach. Cities, 31, 177–185. urban forms. Ecological Indicators, 76, 71–80. Vitali, A., & Billari, F. C. (2017). Changing determinants of low fertility and Reher, D. S., & Iriso-Napal, P. L. (1989). Marital fertility and its determi- diffusion: A spatial analysis for Italy. Population, Space and Place, 23(2), nants in rural and in urban Spain, 1887–1930. Population Studies, 43 e1998. (3), 405–427. Vobecká, J., & Piguet, V. (2012). Fertility, natural growth, and migration in Roca Cladera, J., Marmolejo Duarte, C. R., & Moix, M. (2009). Urban the Czech Republic: An urban–suburban–rural gradient analysis of structure and polycentrism: Towards a redefinition of the sub-centre long-term trends and recent reversals. Population, Space and Place, 18 concept. Urban Studies, 46(13), 2841–2868. (3), 225–240. Rodriguez-Rodriguez, V. (2000). The seven demographic Spains. Inter- Westerink, J., Haase, D., Bauer, A., Ravetz, J., Jarrige, F., & Aalbers, C. B. municipal contrasts in age structure: Fertility and migration are the E. M. (2013). Dealing with sustainability trade-offs of the compact city determining factors. Espace, Populations, Sociétés, 18(3), 425–435. in peri-urban planning across European city regions. European Planning Roig, M., & Castro Martín, T. (2007). Childbearing patterns of foreign Studies, 21(4), 473–497. women in a new immigration country: The case of Spain. Population, You, H., & Yang, X. (2017). Urban expansion in 30 megacities of China: 62(3), 351–380. Categorizing the driving force profiles to inform the urbanization pol- Rontos, K., Grigoriadis, S., Sateriano, A., Syrmali, M., Vavouras, I., & icy. Land Use Policy, 68, 531–551. Salvati, L. (2016). Lost in protest, found in segregation: Divided cities Zambon, I., Serra, P., Sauri, D., Carlucci, M., & Salvati, L. (2017). Beyond the in the light of the 2015 'Oki' referendum in Greece. City, Culture and ‘Mediterranean city’: Socioeconomic disparities and urban sprawl in Society, 7(3), 139–148. three southern European cities. Geografiska Annaler: Series B, Human Rosti, L., & Chelli, F. (2009). Self-employment among Italian female gradu- Geography, 99(3), 319–337. ates. Education and Training, 51(7), 526–540. Zhang, Q., & Su, S. (2016). Determinants of urban expansion and their Rosti, L., & Chelli, F. (2012). Higher education in non-standard wage relative importance: A comparative analysis of 30 major metropolitans contracts. Education and Training, 54(2–3), 142–151. in China. Habitat International, 58, 89–107. Sabater, A., & Graham, E. (2019). International migration and fertility variation in Spain during the economic recession: A spatial Durbin approach. Applied Spatial Analysis and Policy, 12(3), 515–546. Salvati, L. (2016). The dark side of the crisis: Disparities in per-capita How to cite this article: López-Gay A, Salvati L. Polycentric income (2000-2012) and the urban-rural gradient in Greece. Tijdschrift development and local fertility in metropolitan regions: An voor Economische en Sociale Geografie, 107(5), 628–641. empirical analysis for Barcelona, Spain. Popul Space Place. Salvati, L., & Carlucci, M. (2016). The way towards land consumption: Soil sealing and polycentric development in Barcelona. Urban Studies, 53 2021;27:e2402. https://doi.org/10.1002/psp.2402 (2), 418–440.