Framing the Debate on Suburbanization in North America and Germany Conceptually—Edward Soja’s Concept of “Regional Urbanization” Revisited

: This article is on imaginaries of the urban. Here, we develop a critical view on urban and regional developments in capitalist countries and scrutinize explanation patterns anchored in a rigid urban–suburban dichotomy that tend to disregard the complex processuality of current urbanization forms. This contribution focusses on the impact societal change has on spatial and societal structures as well as on forms of socialization in urban regional contexts. As a starting point, we deliberately address current debates on suburbanization from which we ﬁrst derive research desiderata and then conceptually position the debate. The main aim of the paper is to underscore the importance of the conceptual debate on postmodern urban development which is inextricably linked with the so-called LA school of urbanism and in particular with Edward Soja. In the conceptual part of the paper, we start from Edward Soja’s concept ( Postmetropolis , 2000) on postmodern urban development in which overarching urbanization processes materialize on a continuum from center to periphery. His theoretical positionings o ﬀ er a number of possibilities for analyzing and interpreting socio-economic, socio-structural, and socio-cultural urbanization processes. Essentially, we are o ﬀ ering a conceptual discussion of current urban regional processes based on Edward Soja’s theorizations (Soja, 2011) that take the socio-structural, socio-economic, and socio-cultural pluralities and complexity of Regional Urbanization into account. We contend that the seminal contribution of Edward Soja lends itself to a comprehensive and up-to-date understanding of processes of urbanization, including suburban developments.


Post-Fordist Regulation Mechanisms: Focal Point Neoliberalism
Neoliberalism has spread around the globe as today's economic foundation and ideology, and it has substantially impacted urban developments. Urban neoliberalism essentially means the development of entrepreneurial cities and is geared towards privatizing public services and commercializing public spaces to satisfy economic efficiency categories. Brenner and Theodore [15] label these developments as Neoliberal Urbanism. Municipal governance is characterized by global hybridization processes, which have led to an enormous variety of regimes [16] (p. 202). Neoliberal strategies, e.g., privatization, commodification, and market deregulation, affect different cultural contexts in many different ways. Numerous scientific studies have shown, however, that neoliberal strategies have polarizing effects on both urban and suburban spaces. Soja summarizes the effects as "unprecedented inequalities, social polarization, obsession with security and surveillance, abandonment of social welfare objectives, withering civil liberties, ecology of fear, and the rising incidence of homelessness and poverty" [5] (p. 463). He even goes a step further in claiming that Regional Urbanization and its global spread form the basis and are the driving forces for the development and dissemination of what he calls Cultural-Cognitive Capitalism (CCC).

Research Agenda
With this contribution, we do not want to take on board all urban regional research; instead, we would like to contribute to a contemporary theorization of the urban. We discuss this topic on general (theorization of the urban) and specific levels (urban development discussions on suburbia) and we focus on the manifold changes in the socio-economic, socio-structural, and socio-cultural situations that are being re-configured and that materialize on the urban regional continuum of center and periphery. We begin with current debates on suburbanization in Germany and North America, derive our research desiderata therefrom, and define its place on a conceptual level. Our starting point is Edward Soja's concept (Postmetropolis) of socio-economic situations in postmodern urban developments that are reflected in urban regional contexts. He was one of the first researchers who employed a critical socio-spatial point of view and his theoretical deliberations offer numerous possible approaches for analyzing and interpreting socio-economic, socio-structural, and socio-cultural urbanization processes. The aim of our contribution is to use a literature-based overview of current developments in suburbanization in North America and Western Europe, especially in Germany. This should then serve as the basis for revisiting the theoretical concept of Edward Soja's Postmetropolis and discussing its critical perspective on Regional Urbanization. With this in mind, the concept of suburbia is used to reflect the dynamic developments in urban areas. The identification of research desiderata on Regional Urbanization rounds off this article.

Recent Urban Development Processes and their Scientific Contexts
Recent scientific debates on urban development processes have especially focused on reurbanization, the revitalization of cities, and an urban renaissance (see, e.g., [17][18][19][20][21]). When widening that focus, debates on Regional Urbanization include topics such as the urban development of suburbia and suburbia's urbanization (see Section 1, 1.1 and 1.2). Those issues are discussed in this section.
In 2016, the Federal Institute for Research on Building, Urban Affairs and Spatial Development (BBSR) dedicated a periodical issue to giving an overview of suburbanization processes in German-speaking areas [22]. The topics concentrated on future developments in suburbia and the different current scientific debates. In 2018, the periodical Spatial Research and Planning dedicated an issue to Suburbanization and Suburbanism [23] from a European and German perspective and in five contributions highlighted the latest topics in suburbanization research, namely European suburbanization processes, planning aspects, "inner-city suburbanization" [24], peri-urbanization, and life cycles as a conceptional explanatory model.
In 2019, the editors Hanlon and Vicino published The Routledge Companion to the Suburbs [25], which covers the range of the latest international discourses on suburban development. This compilation comprises five chapters and addresses definitions, suburbanization in a global context, social diversity and exclusion, planning, and finally the question on suburbia's end is posed. In the last few years, global perspectives on urban development have become more prevalent in the scientific debate and research on suburbanization in particular has produced a number of papers. In 2018, Roger Keil published the book Suburban Planet [26], in which he gives an overview on suburbanization and explicitly addresses the phenomenon of "Global Suburbia".
In 2019, Güney, Keil and Üçoglu published the anthology Massive Suburbanization [27], which focuses on housing and which identifies changes in urban peripheries across the globe acknowledging the many different contexts and constraints these processes are taking place in. We would like to especially mention the international research project Global Suburbanisms [28] conducted at York University in Toronto under the direction of Roger Keil including many international partners. It explicitly focuses on the global dimensions and features of suburbanization and suburbanism and is the first research project that studied suburbanization processes on all continents. The various research projects analyzed those processes from many different angles and paid special attention to the situation in the Global South. Exemplary for the Global South, Gilbert summarizes suburbia in Latin America as a "rapid increase in urban populations during the twentieth century, allied to improved transport and infrastructure provision, guaranteed that all urban growth took the form of suburban development. Of course, Latin American suburbia is highly diverse, ranging from elite neighbourhoods to flimsy self-help settlements. But it is difficult to argue that it has made much difference to social segregation, insofar as Latin American cities have always been among the most unequal places on earth" [29] (p. 234).
In this context, Short explains that "(s)uburbia, an American myth, became a global yard-stick, to measure and explain suburban experiences and understand metropolitan dynamics around the world. Suburbia has passed into legend. We now live in a global suburbia of greater heterogeneity and difference" [30] (p. 336) (original emphasis). Suburbia, however, is not only a yardstick but also a global phenomenon, as the above-mentioned scientific studies have shown, and depending on each national and regional context suburbia is very differentiated. This led De Vidovich to point out that the term "suburban" actually is not a "one-size-fits-all term" [9] (p. 8) but that it has become evident that the term needs to be the subject of thorough, worldwide scientific research studying multi-dimensional processes along the "urban edges" [9] (p. 8). He goes on to conclude that "[ . . . ] to investigate societal changes, rather than pursuing an unruly usage of the concept of "suburb" to describe what stands beyond the city [ . . . ]" [9] (p. 8) (original emphasis).
To some extent, such societal changes are reflected in debates on urban development processes, e.g., in quantitative-empirical studies using measurable variables. Studies on the German situation have shown that principally re-and suburbanization processes happen at the same time. Milbert [31] found that the centers of large cities mostly register an increase in inhabitants, while at the same time urban-suburban migrations of families are registered. Münter and Osterhage [32] focused their study on three central phenomena: reurbanization in small-and mid-sized cities, "spill-over effects" (translated by the authors) in large cities, and depletion of rural areas. The authors essentially ascertained reurbanization tendencies also in medium-sized cities and larger small-towns in rural areas. In regards to large cities, the authors observed "spill-over effects" [32] (p. 14). They note that "especially in large cities that lately have been subjected to reurbanization processes the capacities to absorb more new comers have become limited and those looking for places to live are 'pushed' to the hinterland" [32] (p. 14) (original emphasis, translated by the authors). The stressed housing market in large cities then becomes the main explanatory factor for the continuous suburbanization processes. In this duality, Münter and Osterhage recognize a "concurrence of large-scale reurbanization and small-scale suburbanization" [32] (p. 16) (translated by the authors).
Considering the situation in the US, Keil states that "[ . . . ] suburbanization continues unabated" [33] (p. 4) and makes reference to a report from Brookings Institution. In that report, Frey points out that "The Census Bureau's annual county and metropolitan area estimates through 2017 reveal a revival of suburbanization and movement to rural areas along with Snow Belt-to-Sun Belt population shifts. In addition, the data show a new dispersal to large-and moderate-sized metro areas in the middle of the country-especially in the Northeast and Midwest. [ . . . ] The new numbers leave little doubt that suburbanization is on the rise, after a decided lull in the first part of the decade" [34] (without page reference).
On a quantitative level, the findings of these studies contribute to answering the fundamental "what" question. They record the current status quo and develop a basis to reconstruct current urban development processes. What they do not achieve, however, is to answer the "how" and "why" questions, i.e., learning about the driving motives and forces behind those processes. Typically, it is of course not the goal of quantitative studies to answer those types of question. On a deeper level, studies of these types reduce the complex phenomena of suburbanization to simple, measurable issues in statistically determined spatial units.

Socio-Structural Changes in Suburbia and Suburbia's Urbanization
Socio-structural changes in suburban spaces cannot be comprehensively understood by studying quantitative data or statistics alone. This is why the following discursive elaborations deal with socio-structural and socio-cultural changes in a more qualitative way. They can be seen as a continuation of the aforementioned quantitative studies but with an emphasis on the "how" and "why" questions.
A starting point for the debate in German-speaking areas is Hartmut Häußermann's article Suburbanization is Running out of its Personnel (translated by the authors), published in the periodical StadtBauwelt in 2009. He points to changing family models and models of life as well as to post-Fordist labor markets and to the growing importance of high-quality services in urban spaces. These phenomena are combined to cross-reference socio-structural and socio-cultural changes in suburbia. Häußermann elaborates that "the number of households no longer following the Fordist standard model when it comes to choosing where to live, is increasing" [35] (p. 53) (translated by the authors). He links socio-structural changes to economic changes and speaks of a "post-Fordist economy" [35] (p. 54). Women's role in society, for instance, illustrates the differentiation and multiplication of lifestyle types and patterns as well as changes in value systems. Häußermann's reference to "personnel" in suburban spaces includes not only the total number of suburban inhabitants but also changes in gender roles and with it the disappearance of the classic housewife as "suburbia's personnel" that is responsible for household and re-production work. The classic family model in which the man was the single breadwinner and which constituted the emergence of suburban spaces is no longer "commonplace" (alluding to "standard biographies" [36] (p. 74) (translated by the authors; see also Section 2.2)). Other contributions also consider the end of this stereotype of suburbia as the onset of hetero-normative life models (e.g., [37]).
In continuation of the multiplication of life models, Menzl [38] concentrates on the question of "urbanization processes in suburbia" and with it an increased occurrence of "urban lifestyles" in suburban spaces, as a reaction to new requirements in post-Fordist societies. Menzl finally concludes that "suburban life styles are not being urbanized" [38] (p. 43 and pp. 58-59) (translated by the authors), i.e. urban lifestyles are not dominant in suburbia and suburban characteristics are upheld there. According to Menzl, these characteristics are "a focus on children; the place of residence as a safe haven; structural, life-cycle, social, and normative homogeneity; safety and security; nature-relatedness" [38] (p. 43 and p. 46-47) (translated by the authors). Menzl, however, does detect a hybridization between "Fordist" and "post-Fordist" plans of life [38] (pp. 49ff.). Residents were not trying to create a "more urban" living environment and, if so, that would not easily be possible owed to local actors holding on to "their tried and tested normative patterns" [38] (p. 58) (translated by the authors) and accompanying resistances. Menzl calls that hybridization as the "entering of a second modern age or a post-Fordist society" [38] (p. 59) (translated by the authors) in suburbia.
In terms of altered lifestyles, Kühne studied changes in San Diego's population structure. There he sees shifts "from traditional families with suburban life and consumption patterns [ . . . ] to an increase in single persons and pairs whose lifestyle and preferences are markedly urban" [39] (p. 27). An "urbanized" suburbia can also be attractive for couples without children or singles who are looking for a "synthesis of suburban comfort and urban opportunities" [39] (p. 28). Kühne also studied the Greater Paris area and reports that "Levallois-Perret a former industrial and working-class area has become a flourishing urban municipality attracting so-called 'yuppies' and 'dinkies' with accommodation tailored to their tastes and expectations, and a lifestyle offer including cafés, boutiques and parking facilities" [39] (p. 30). In this case, Kühne [39] makes explicit reference to the Young Urban Professionals' models of life as well as to that of double income couples without children. These socio-structural and socio-cultural changes are incidentally linked to the restructuring of the physical-material environment and Kühne goes on that "(f)inally, Levallois-Perret exemplifies a residential quarter whose prior physical structures have been replaced wholesale by new ones that have brought with them corresponding changes in use [ . . . ]" Kühne [39] speaks of this "urbanized" suburbia being more and more fragmented and he sets his elaborations in the context of postmodern urban development.
Next to recognizing differentiated models of life, ethnic aspects play an important role when studying suburban spaces from a qualitative perspective. In the German-speaking debate, ethnic aspects are seldom included, whereas in the US debate they have played a role for a long time. In The New Suburbanites: Race and Housing in the Suburbs Lake [40], for instance, connected the suburbanization of the black population to inequality and discrimination. In her contribution The New Sociology of Suburbs, Lacy [41] points out three central trends that highlight why ethnic aspects once again need to be included into current research projects: "the suburbanization of poverty, the settlement of post-1965 immigrants in the suburbs, and the impact of reverse migration to the South on black suburbanization" [41] (p. 369). Accordingly, in the US debate, "immigrant suburbs" are also addressed: "Immigrants now live in suburbs as well as cities" [42] (p. 150). The focus there when discussing socio-structural, socio-cultural, and economic changes is much more on inequality, exclusion, or poverty.
In 2015, Anacker published an anthology titled The New American Suburb. Poverty, Race and the Economic Crisis [43] dedicated to those topics. Gallaher's contribution in that anthology is on the situation in the Washington D.C. Metropolitan Area, for which she states that "(c)lusters of people who define themselves as Black/African Americans, for example, are now more likely to be located in suburban locales than inside city limits. The same is true for Latino population clusters [ . . . ]" [44] (p. 107) and continues: "[ . . . ] there are still racial/ethnic dividing lines in places across the entire metropolitan area. The Black/African American population, for example, has suburbanized, but Blacks continue to cluster apart from non-Hispanic Whites" [44] (p. 107).
In the same anthology, Beck Pooley [45] observes that: "non-Hispanic White home-owners and homebuyers tend to prefer units in predominantly non-Hispanic White neighborhoods and therefore choose to move out of, or not move into diversifying neighborhoods" [45] (p. 74). She goes on to show how strongly poverty and its manifestation can vary depending on each suburban space, and distinguishes five different "census tracts" for scaling poverty. Beck Pooley explains that "(l)argely Black/African American suburban communities typically bear the unfair burden of decades of discriminatory practices and the lager market's undervaluing of their properties" and that "[ . . . ] median property values in most Black/African American communities remain low and stagnant" [45] (p. 74).
In 2019, Anacker stresses that the effects of recent financial crises pose new challenges for the state-institutional level because "(i)n the coming years, income and wealth inequality in mature suburbs will most likely increase [ . . . ]" [46] (p. 215). She also points out that, beginning in the 2010s, the term "poverty" is being "explicitly acknowledged and discussed" [46] (p. 210) regarding suburbia. "Inequality" and "poverty" as elements originally associated with cities have now also moved into suburban spaces. These spaces used to be characterized by white middle-class small families but now they are more and more confronted with questions of equal opportunities and social justice. However, the situation in suburban spaces differs from those in "poor" downtown districts. Anacker points to social service shortcomings by stating that "(o)ver time, the number of suburban residents in need has increased, but the number of service providers' offices in the suburbs has remained steady or declined, resulting in a spatial mismatch in social service provision" [46] (p. 212).
It can be concluded that socio-structural and socio-cultural changes in suburbia are not only owed to changes in ways of living and lifestyle models that are owed to societal changes, but also to ethnic and economic differences and that they need to be taken into account as well.
In conjunction with analyzing socio-structural and socio-cultural changes, here we include the discussion on post-war single-family homes in Germany, especially those built between the 1950s and 1970s. Münter [47] refers to the demographic change moving into suburban spaces. The debate focuses on older single-family homes characterized by the younger generation moving out and leaving the older generation, i.e., empty nesters, behind. In corresponding publications, this type of single-family home is typically described as a planning challenge and new possible uses and planning instruments are being discussed (e.g., [48][49][50][51]). However, several important socio-structural, socio-cultural, and socio-economic questions are connected to these changes. Principally, the generational change can lead to rejuvenating suburban neighborhoods, if the younger generation remains in suburban single-family homes. It is possible that suburbia could be heterogenized when people whose lifestyles do not resemble the suburban stereotypes move to suburbia. Moves of these types could be induced when people originally living in suburbia move to downtown areas (see reurbanization discourse) because their lifestyles changed, thus opening the possibility that "new" interest groups could move into those single-and double-family homes.
The consequences of these changes are not only evident in suburban spaces; reurbanization tendencies are also discussed in connection with older population parts returning to downtown areas (e.g., [52]). Single-family homes specifically cater to the needs of small families, not only in suburbia. Given the growing number of one-person households, however, it is unclear which "new" user groups could be attracted to moving into older single-family homes.
Socio-economic and socio-structural changes in suburban spaces are also connected to changes on the housing market. The German Economic Institute points out the continuously increasing prices of single-family homes from 2013 to 2018 and identifies the development of interest rates (financial feasibility and lack of investment alternatives) as well as a growing influx into metropolitan areas and high real-estate prices in large cities as reasons for this development. The authors also highlight how it has become more difficult to own property, for instance due to high capital requirements [53]. Changes on the housing market are not only owed to simple causal connections of socio-structural and socio-cultural changes in suburbia. However, from a practice perspective, it must be kept in mind how the price level affects the housing demand in suburban spaces, in the hinterlands, and in urban spaces, especially when recalling the abovementioned "spill-over effects" and ethnic and "financial" heterogenization of suburban spaces. Aside from rising prices for single-family homes, Brombach et al. note that, in "recent years, the core cities' housing markets have increasingly priced out low and middle-income households". In this trend, the authors recognize the possibility "[ . . . ] for a certain revival of suburbanization" [19] (p. 311).

Suburbanism as a Way of Life
What the debates discussed here have shown is that suburban spaces are (discursively) associated with a specific lifestyle, a lifestyle, however, that is subjected to socio-structural and socio-cultural changes. In the German debate, neither suburbanism nor "suburbanization of lifestyles" has received particular attention, notwithstanding German-speaking contributions have included those terms starting in the mid-20th century (e.g., [54]). Gans [55] took the topic up in conjunction with an article by Wirth titled Urbanism as a Way of Life [56] (originally 1938). Gans' text can be understood as a fundamental text on the topic of lifestyles in downtown areas, the "outer city and the suburbs" [55] (pp. 74ff.) (translated by the authors) and their respective stereotypes. Generally, the term suburbanism is seldom used in the German debate; Häußermann and Siebel, however, are an exception. In their book on Urban Sociology (2004), they dedicate a six-page chapter to the term suburbanism. There they stress a specific suburban way of life that is characterized by being centered around the family and a life with children. This leitmotif is especially typical for the time after World War II and was considered to be a "normal or standard biography" [36] (p. 74) (translated by the authors). Häußermann and Siebel also stress the elements "privatism and familyism" [36] (p. 76) (translated by the authors) that are connected to suburbanism. In current publications, special reference is made to "suburban ways of living", sometimes with a focus on "Heimat", i.e., belonging to suburban spaces [57].
Robert Fishman deserves special mention when turning to Anglo-American research. In his book Bourgeois Utopias: Visions of Suburbia published in 1987, he refers to suburbia as a "cultural creation" [58] (p. 8) and as the decisive decision for a specific way of life connected to suburban spaces. "The emergence of suburbia required a total transformation of urban values: not only a reversal in the meanings of core and periphery, but a separation of work and family life and the creation of new forms of urban space that would be both class-segregated and wholly residential. Who then invented suburbia and why? To ask the question is to formulate a major thesis [ . . . ], which is that suburbia was indeed a cultural creation, a conscious choice based on the economic structure and cultural values of the Anglo-American bourgeoisie. Suburbanization was not the automatic fate of the middle class in the 'mature industrial city' or an inevitable response to the Industrial Revolution or the so-called transportation revolution" [58] (pp. 8-9) (original emphasis).
Walks on the other hand approaches suburbanism from a theoretical perspective and sets up a "conceptual grounding" [59] (p. 1472). As a starting point, Walks chooses Lefebvre's concept of space and based on an "urbanism-suburbanism dialectic" [59] (p. 1471) describes six dimensions of this dialectic. The different dimensions interact with one another and are connected through a "productive tension" [59] (p. 1479), thus enabling numerous different "suburbanisms" [59] (p. 1483), i.e., ways of life. Walks finally summarizes "[ . . . ] urbanism-suburbanism. The latter is understood as the meta dialectic producing new, hybrid, ways of life in the contemporary metropolis" [59] (p. 1485) and continues that "(t)hese theoretical dimensions of urbanism and suburbanism are therefore conceptually separate from the grounded areas of settlement known as cities and suburbs" [59] (p. 1485).
If we follow the thought that suburbanization as a way of life (in the sense of suburbanism) can be separated from the original connectedness to spatial units, then the question arises if those forms of suburbanization can also be found in urban (downtown) spaces. This question is linked to the qualitative aspects on the "how" and "why" mentioned in the previous section and extends the issue of suburbanization to cities themselves.
The debate on the suburbanization processes in (core) cities is mainly led by Frank (e.g., [24,60,61]). Frank is primarily concerned with the "new middle-class" [61] in cities, in suburban "enclaves" [60]. To her understanding, reurbanization is not limited to quantitative migration determinants but also includes qualitative aspects. She recognizes classical characteristics of "suburban ideals" [60] (p. 25) in downtown areas and especially refers to life and lifestyles of families in downtown areas. Her starting point and basis are Lefebvre's works and her understanding of suburbanism as an expression of a specific way of life (see [59]) and she coins the expression "inner-city suburbanisms" [24]. According to Frank, the categories "urban" and "suburban" no longer represent the lifeworld and socio-structural distinctions between the different sub-spaces of the urban region. She sets her distinction between "urban" and "suburban" clearly apart from a spatial definition and suggests that "(i)f we focus on urbanism and suburbanism as ways of life that are not bound to a specific location, we are much better prepared to understand the fragmented nature of today's metropolitan regions as a patchwork of spaces whose different parts are the product of the varying tensions and interactions of the forces or flows of urbanism and suburbanism [ . . . ]" [24] (p. 130). Other authors also contribute to this debate. Menzl [38], for instance, speaks of a hybridization of lifestyles, as discussed above. Mölders et al. [62] point out spaces' hybridity and address the "coexistence of urban and suburban ways of life" [62] (p. 42) (translated by the authors).

Economic Processes in (Sub-)Urban Developments
Change processes, however, do not only become evident in socio-structural and socio-cultural factors. In the past years, suburban spaces often have also been subjected to economic changes, e.g., industries and services moving to commercial and business areas outside of town. These developments, however, are not new. In 1975, von Rohr [63] (industry suburbanization) and Hellberg [64] (suburban service locations) studied them in Germany. In a more recent contribution, Jansen, Roost, and Wünnemann published an article on Office Parks in the Rhine-Main Area [65] (title translated by the authors). By analyzing two example cases, the authors addressed the challenges and possible actions when dealing with changing framework conditions for (older) service locations in suburban spaces. They also make reference to the US debate on Edge Cities, to the demand for suburban housing, and to the idea of mixed uses instead of a strict functional separation in suburban spaces. They argue for a long-term, strategic linking of social and economic factors. This is why in recent quantitative studies there is also a focus on the development of employment and land (see also [66]).
In her current publication, Adam [67] conducts a multi-dimensional, quantitative study on suburbanization, in which she indexes suburbanization processes along three features: population, employees, and land. Her results show that the population development in large cities can be described in terms of reurbanization but that the development of land and employees instead offers a "heterogenous picture" [67] (p. 52) (translated by the authors).
The need to link social and economic changes can also be seen when turning to changes in spatially based lifestyles, as discussed in Section 2.1. Häußermann [35] and Menzl [38] point to changes in the labor market (in terms of post-Fordist re-structuring) and how they impact the concrete, personal life situations of "classic" suburbanites. Impacts could, for instance, be more flexible working conditions that do not allow long-term life planning at one place, university degrees that are possibly more and more required for finding a job, or a single principle occupation that is no longer sufficient to support a family because the financial demands on suburban life models have increased.
In a sense, the term Edge City is a synonym for those economic-structural changes in suburbia. It was especially Garreau who coined that expression in his book Life on the New Frontier in 1991. He bases his observations on the development in US cities and defines an Edge City as a location that competes with the downtown area or central business district and that can be described as a functional location beyond city limits. The criteria that characterize an Edge City include the availability of retail and office spaces as well as a dominance of work places over "bedrooms" [68] (pp. 6-7). Garreau also addresses societal structures and their dynamization caused by the described spatial developments and he remarks that "(f)irst of all, edge cities are female, and downtowns are male" [69] (without page reference). He identifies two causal factors for these developments and notes that "[ . . . ] these places have lots of elderly residents, and women tend to live longer than men. The general pattern is that women choose to live in safe, small-to-medium-sized urban cores, many of which also attract older people" [69] (without page reference). Historically, he also sees a close connection between the emergence of Edge Cities and the "empowerment of women" [68] (p. 111). The shift from a male principal earner to two earners with both the man and the woman contributing to household earnings, i.e., the realignment of gender relations, was facilitated by employment opportunities in Edge Cities. Garreau notes that the socio-economic structures of Edge Cities are characterized by entrepreneurs and small companies that employ highly qualified personnel, which in turns means that above average incomes can be generated in Edge Cities. Edge Cities to Garreau are symbols of the future urban development in the US, whereas core cities to him in a sense seem somewhat outdated.
These economic changes also entail functional expansions in suburbia as described in the terms post-suburbia and post-suburbanization, respectively. With regard to the situation in Germany, Brake, Dangschat, and Herfert [70], for instance, discuss "center qualities" [70] (p. 7) (translated by the authors) that emerged in suburbia and that created "new locations for consumption" (translated by the authors) that can be found in suburban spaces. At the same time, this addresses a more pronounced decoupling or revision of formerly strict dependencies on core cities. Knapp  Parallel to the physical-material changes, suburban spaces along the (former) urban periphery have been and still are experiencing a functional revaluation in connection with the economic restructuring, thus developing new qualities in suburbia. However, it might be just these economic changes and functional expansions that generate those "new" or "hybrid" life plans and that contribute to suburbia's revaluation.

Definition and Delineation of Suburban Spaces
The just described recent urban development processes and the subsequent changes impacting suburbia lead to the question of how suburban spaces are defined and situated in the scientific debate. Typically, neither the quantitative nor the qualitative debates explicitly offer decisive definitions or put forward their territorial understanding of the spatial; instead, a general understanding of suburban spaces is assumed These terminological ambiguities concerning suburban spaces and suburbia are especially apparent when reviewing the very different publications. To Phelps, the terms suburban and city are "deceptive terms" and he pointedly remarks that "(t)hey are both difficult to define precisely and are rather more a case of 'we know one when we see one'" [72] (p. 40) (original emphasis).
Why, however, is this relevant for this contribution? As mentioned at the beginning, we are concerned with our imaginaries of the urban. Huq's list, as presented above, illustrates the specific characteristics associated with "suburban" and "inner city/urban". These stereotype attributions shape our images on suburban as well as on core city spaces. Thus, identifying how each author actually defines suburbia is anything but "trivial". Even the simple seeming question of "How many people live in suburban spaces?" (see [73] (p. 17) for rural areas) illustrates this. Based on the just discussed socio-structural, socio-cultural, and socio-economic changes, we now shortly mark the range of the term's usage.
The German-speaking literature lacks a detailed study on the delineation and definition of the term suburban spaces (an exception might be found in [74,75], which both give an overview of the understanding of the term). The English-speaking literature situation is different. Forsyth [76,77] in detail studied the various definitions and interpretations of the term suburb and categorized them into five "dimensions": "physical (where, what); functional (operations); social (who); process (how, when); analytical" [77] (p. 16). Forsyth finally recommends how to use this spatial category in the future by suggesting to either relinquish the term, to replace it, to accentuate its particular features, or to keep the term but to typify it by determining set categories [77] (p. 25). De Vidovich demonstrates the wide variety in which the term is already being used and summarizes the different terms and definitions by authors and research cultures [9] (p. 6). Walks furthermore collected numerous descriptions for the term suburbia, e.g., "technoburbs' (Fishman, 1987 Overall, the academic understanding of the term suburban spaces is incongruent and heterogeneous, not only on a global scale. Occasionally, there are academic papers that point out these definition ambiguities (see, e.g., [75,78,79]). There are, however, approaches to typify suburban spaces along structural, economic, and other criteria (see, e.g., [80,81]).
Official organizations, too, often lack a definite understanding of the term. Beck Pooley points out that the U.S. Bureau of the Census does not have a set definition of the term suburbia [45] (p. 39) (see also [77] (p. 19)). The situation is similar in Germany, where official organizations also do not operate with a set definition.
Mutschler [78] goes as far as to describe suburban spaces as chaotic constructs, based on the addressed socio-structural, socio-cultural, and socio-economic changes and the diversity and ambiguity of spatial terms connected to them. He concludes that "suburbia presents itself to observers as a seemingly orderless patchwork of historic village centers, post-war single-family home settlements, high-rise districts, clusters of large-scale elements such as commercial areas or recreation centers, technical infrastructures and traffic routes as well as atomized residual agricultural areas and clearances. The classic dichotomy between city and village on the outskirts of cities has long gone, the boarders have become fluid, the contours of a city are no longer tangible. What is perceived is a mosaic of urban fragments and urban islands" [78] (p. 330) (translated by the authors). On the one hand, this citation demonstrates that the suburban space is not a distinct, homogenous space; on the other hand, it points to the necessity of considering this "seemingly orderless patchwork" conceptually and of classifying it.

Interim Conclusion: Research Perspectives, Central Themes, and Conceptualizations
What conclusions can be drawn from this cursory recapitulation of selected debates? The selection was deliberate and was geared towards central urban development topics and their respective research strands, especially questions related to socio-structural and socio-cultural differentiation processes in Regional Urbanization contexts. We therefore cannot and do not want to claim that we completely covered all authors, research contexts, and research cultures concerned with "urban", "suburban", and Regional Urbanization; that notwithstanding, it is our goal to highlight the scientific debates' plurality on those topics.
Quantitative studies offer an overview on urban development processes and are important for reaching (valid) statements on empirically verifiable phenomena in urban regional contexts. For Germany, for example, we can see that sub-and reurbanization are taking place at the same time and that their developments depend on the spatial level and the specific local conditions. Qualitative studies on socio-cultural changes should, especially when studying German-speaking literature, be more in-depth and take aspects into account that to date have received only little attention, e.g., migrant's suburban lifestyles and in particular the lifestyles of second, third, or fourth generation migrants. Another aspect to be studied more in-depth could be further differentiating Menzl's [38] hybridization of lifestyles or the observations made by Kühne [39] on double-income, childless couples moving into (former) suburbia. Studies that focus on such qualitative aspects provide insights to the readers as to the "how" and "why" of suburban spaces' socio-structural and socio-cultural continuous differentiation. The debates on suburbanism (see Frank's "inner-city suburbanism" concept [24]) point to the meaning spatial categories have when studying current trends in urban regional contexts. Studying suburbanization as an expression of a specific way of life opens new perspectives for our understanding of urban development and, again, illustrates the need of a possible further differentiated understanding of "suburbanism".
The debates on economic developments have shown how important it is to include societies' economic dynamics when studying urban development in a Regional Urbanization context, not least because economic processes are also responsible for structural changes in suburbia and should therefore be included when studying societal processes. This is especially true since the suburban space has structurally been amplified and changed through these economic restructurings and, as Frank [24,82] stresses, initiates socio-structural changes and as a result also brings about paradoxes.
However, many debates lack a classification of general urban development concepts and theories and, consequently, a basic discourse on the conceptual definition of development processes in a Regional Urbanization context. In the following, we set out to show if and how these processes can be brought together on a conceptual level to contribute to a better overall understanding and to point to other, still open research questions. After all, in the past few years, the question about the end of suburbia has continuously been raised (e.g., [30,83]); Lütke and Wood [11] brought forward the question of "new" suburbia). Short follows the idea of a suburbian ideal and pointedly explains-here in connection to socio-structural changes-that "(t)he real question is not whether a myth is true or not but whose truth it is" [30] (p. 336) and later "(r)ather than a place of Being, it is still in the process of Becoming" [30] (p. 336)-meaning suburbia. On the one hand, this encapsulates the understanding that the suburban space reflects the ideal of certain societal groups; on the other hand, it acknowledges that the suburban space is constantly changing and that it therefore cannot be viewed as a delimited (spatial) entity and that other and new societal groups can be found there. Short summarizes the current developments, among other things, with the end of single-family homes dominating suburbia, a clearly more heterogeneous social structure instead of only white middle-class and that spaces for working and living are no longer strictly separated. What is even more important is his assessment that the dissolution of the classic urban-rural dichotomy into an urban continuum does not allow referring to suburbia as a singularity (p. 340). He concludes that "(i)t is the end of the suburbs as a phenomenon and suburbia as a useful discursive device. Our task is now to build more sophisticated models and understandings of a complex metropolis without the crutch of these increasingly obsolete terms" [30] (p. 340).
This pointed conclusion can serve as the starting point for settling the issue whether to talk about the end of suburbia and the end of the suburban spaces, respectively or, in the light of structural changes, to talk about "new" suburban spaces. The discussed debates also show that, in light of the societal developments in urban regional contexts, the traditional notions of suburbia need to be questioned. Thus, it seems to be more expedient to talk about a post-suburbia since these spaces no longer correspond to the stereotypes that once described those spaces. "In a nutshell, post-suburbia is a key to understanding contemporary suburbanization in its heterogeneity [ . . . ]" [9] (p. 8). The above-described change processes permeate suburban spaces in the course of Regional Urbanization and point to a physical-material, socio-structural, socio-cultural estrangement of the original term suburbia and to the question of post-suburbia's conceptional placement in today's urban development theories.
To create a more deep-seeded understanding of the different aspects of Regional Urbanization, several studies introduced here derive theoretical-conceptional connections. Walks [59] and Frank [24] suggest to view suburbanization as both a product and a negation of urbanization [24] (p. 125). Following Lefebvre, Walks also suggests to theorize the forces creating the tension between urbanism and suburbanism as "(f)lows that move in and through particular places and spaces, inhabiting them for distinct yet indeterminate lengths of space and time" [59] (p. 1477). His reasons for taking such a perspective are conceptual arguments. Both Walks and Frank suggest to separate societal processes from spaces thus leading to more clarity in the debate and to a pluralization of (sub)urbanisms: "We can thus imagine a vast variety of possible (sub)urbanisms" [59] (p. 1478).
The theory of regulation addresses the interplay between economic, social, and political structures as well as societal negotiation mechanisms, differentiation of lifestyles, and spatial correlations between these developments. Several studies have analyzed these connections; Frank [82] focusses in particular on inner-cities, while Menzl [38] on hybrid lifestyles.
When studied from this theoretical perspective, societal developments can be contextualized chronologically or historically, thus enabling a deeper understanding of socio-spatial development tendencies. It also enables conceptualizing the complex interaction patterns on which societal developments rest in a more consistent manner. In his studies on urbanization processes in suburbia, Menzl [38] turns to Beck's construct of "reflexive modernization" [84]. This allows him to theorize on the growing socio-structural complexity of life plans in many "Second Modern Age" (translated by the authors) households. Menzl then concludes "that post-Fordist changes have led to changes and realignments in suburbia but that neither the term urbanization nor the ongoing processes in suburbia is done justice when referring to suburbia's urbanization on the level of normative orientations and ways of life" [38] (p. 58) (translated by the authors).
These cursory remarks on the conceptual deliberations are meant to reflect the authors attempts to offer an in-depth understanding of the changes Regional Urbanization is undergoing. What also becomes evident, however, is that this by no means is a comprehensive theoretic offer in the sense of a "grand" urban development theory. Given the heterogeneity and complexity of the observed phenomena in socio-spatial developments, this is certainly not surprising. However, the question remains whether a comprehensive theorization of (sub)urbanization tendencies is possible and what it could look like. That is the question we try to answer in the next section.

From Metropolitan Urbanization to Regional Urbanization
In his contribution Regional Urbanization and the End of the Metropolis Era [1], Soja declares the end of modern day's metropolis era and the beginning of the Regional Urbanization era. Characteristic for this new era is that cities and suburbia are interlinked in complex ways. Metropolitan Urbanization is connected to industrial capitalist urban development and is followed by Regional Urbanization. The (demographic) explosion of city centers starting in the 1960s is seen as a turning point because it was then that the density gradients in urban regions began flattening out over time and categoric distinctions between urban subspaces increasingly was less possible. "The flattening out and extension of the density gradient points to the increasing erosion of the formerly relatively clear boundary between the urban and the suburban, a marked homogenization of the urban landscape from center to periphery" [1] (p. 11). This trend reflects the emergence of polycentric networks in urban agglomerations with a comparatively high population density. Urban peripheries become laced with edge cities, outer cities, boomburbs, metroburbia, hybrid cities, urban villages, etc.
According to Soja, this process leads to an increase in suburbia's urbanization [1] (p. 6) and/or to Regional Urbanization processes [1] (p. 7). He explains this development trend with three driving forces: globalization of capital, labor, and culture; economic structural changes and New Economy's emergence; and the effects of new information and communication technologies. Soja also identifies transnational migration as a driving force especially in metropolitan cores. These developments lead to the disappearance of the urban-suburban duality in academic debates and they open new perspectives that will also transcend the boundaries of Regional Urbanization. In this context, he addresses the development of so-called mega city regions with ten to fifty million inhabitants as well as urban "galaxies" with more than 250 million inhabitants [1] (p. 10).

Postmetropolis-Urban Development Trends and their Theorizations
Soja's assessment of urban development trends and their conceptual classification can be placed in a larger discursive frame and he derives this in his comprehensive monography Postmetropolis [7], which in a broader academic sense can also be referenced to the L.A. School of Urbanism. In addition to Edward Soja, other L.A. School academics are Michael Dear, Allen J. Scott, and Michael Storper. Their main focus is on identifying the connections between the new urbanism types and general societal development trends in order to develop contemporary theories on urban changes. Both Soja's and Dear's research is focused on Los Angeles since they believe that postmodern trends in urban development are ideally and typically represented there and that Los Angeles therefore can serve as an important starting point when analyzing other cities and city regions.
In Postmetropolis, Soja scrutinizes the theoretical placement of the latest urban development processes. Given his differentiated and detailed reasoning structure, his findings continue to be of great valuable for today's debates. In his accounts on Postmetropolis, he conflates six discursive strands: One of the central presuppositions in many studies on the dynamics of urban change is that urban development in capitalist societies can only be adequately understood when society's economic basis is explicitly included. Therefore, it does not come as a surprise that Soja also places a strong emphasis on the connection between economic and spatial restructuring in his conceptualization of urban change; a topic he discusses in the first two discourses (Chapter 6: Postfordist Industrial Metropolis and Chapter 7: Cosmopolis [7]). He takes on board central elements of regulation theory and he also includes the globalization and neoliberalization discourses in order to permeate the described change tendencies in city systems and in cities on a theoretic-conceptual level.
The next two chapters (Chapter 8: Exopolis and Chapter 9: Fractal City [7]) then draw attention to the spatial and socio-structural consequences of postmetropolitan restructuring. The chapter on Exopolis concentrates on spatial changes and Soja discusses the complex spatial change tendencies. These tendencies challenge conventional urban geography perspectives on urban changes since decentralization and re-centralization processes-from inside-out and outside-in-defy established patterns of the urban.
The chapter on Fractal Cities examines in great detail the complex forms of socio-spatial fragmentation and polarization as well as the emergence of hybrid forms in social space. Postmodern cities also include areas that to a degree are extensive, i.e., areas that are impoverished due to economic and socio-economic restructuring and that stand in stark contrast to areas of prosperity, abundance, and consumption. The latter can be found both in neighborhoods inside the city limits, often in the periphery (suburbia), and in so-called post-suburban developments (Edge Cities).
These changes are often discussed in a wider context in (German) urban sociology. As early as 1998 [85], Häußermann postulated that the cities of the 19th and 20th centuries had lost their role as an "integration engine" (translated by the authors) and that this was owed to economic, political, and demographic change tendencies. Urban societies had changed in many different ways: the labor market, for instance, had become saturated and closed for many; social buffers in housing stocks had declined and providing for housing had more and more become subjected to market dynamics; and urban societies had grown to be ever more heterogenous and ethnically differentiated.
The last two chapters of Postmetropolis are concerned with power/control (Chapter 10: The Carceral Archipelago [7]) as a reaction to the "Ecology of Fear" (translated by the authors) and with the changed perspectives on the urban as they are, inter alia, facilitated and brought about by the electronic media (Chapter 11: Simcities [7]).
The reasons to revisit Soja in this contribution are twofold. First, he emphasizes the close connection in and between the six discourses and the necessity to establish the connections between the discourses. Second, he addresses the growing economic, social, and cultural heterogeneity in urban spaces. When looking at the close connections between the discourses, Soja points out the mutual references between the empiric phenomena and their conceptual classification, also across the discourses. He goes on to stress that it is necessary to include these mutual references in order to adequately account for the complexity of the developments in postmetropoles. Among other things, he sees a close connection between the discussion of urban forms and the fragmentation of the social and/or social spaces in the city (Chapters 8 and 9) and the debate on economic restructuring of the urban (Chapters 6 and 7).
Although the theoretical positionings he undertakes do not result in a "grand" theory of postmodern urban development, they are an inspiring, albeit somewhat eclectic, foray into the sociological theories of the late 20th and early 21st century. To this day, they are exemplary for sophisticated conceptual foundations of urban development debates. We would now like to briefly illustrate this by discussing the concept of post-suburbia.
In Chapter 8, Soja elaborates: "(t)he urbanization of suburbia and the growth of Outer Cities has generated its own tracks of reconceptualization, not just of the erstwhile suburban milieu but of the modern metropolis as a whole. In recent years, postsuburbia has emerged as one of the catchall terms, with Orange County, the heartless center of postsuburban California (Kling et al., 1991), as its most representative case. There are other descriptive metaphors: 'the metropolis inverted', 'the city turned inside-out', 'peripheral urbanization', and, in a more comprehensive sense, the term postmetropolis itself. What all these descriptions share, implicitly or explicitly, is the notion that the era of the modern metropolis has ended" [7] (p. 238) (original emphasis). These thoughts on the end of modern metropolis are referenced back to Chapter 6 (here especially back to regulation theory and the corresponding spatial patterns in "Fordism"), where he states that "Fordism simultaneously accentuated centrality, with the concentration of financial, governmental, and corporate headquarters in and around the downtown core; and it accelerated decentralization, primarily through the suburbanization of the burgeoning middle class, manufacturing jobs, and the sprawling infrastructure of mass consumption that was required to maintain a suburban mode of life" [7] (p. 239-240).
Soja also pursued the intention to set himself apart from other discussants and to repudiate outdated or problematic classifications of urban development. This includes not only the Chicago School of Urban Ecology but also newer contributions on urban development. Soja breaks with Chicago School's perceptions of urban development by challenging their mono-centric urbanism, and he writes that "emphasizing the new while recognizing the persistence of long-established geohistorical trends, it can be argued that during the past thirty years the growth of Outer Cities has both decentered and recentered the metropolitan landscape, breaking down and reconstituting the prevailing monocentric urbanism that once anchored all centrifugal and centripetal forces around a singular gravitational node" [7] (p. 241-242). The Chicago School's approach is characterized by simple center-periphery patterns or by spatial patterns in form of concentric circles or sectors; this approach therefore does not allow to react to the ever-growing complexity in current urban development trends.
When turning his attention to newer urban development concepts, Soja [7] (pp. 243ff.) (see also Section 2.3) paid special attention to the concept of Edge Cities, developed by Garreau [68]. According to Garreau, the "suburban trap" (translated by the authors) for women had turned into an "Edge City Liberation" [68]. Soja denounces this view as a case of spin-doctoring to confer a positive picture of Los Angeles [7] (p. 245). Frank [82] (pp. 143f.) also takes a negative view on Garreau's concept and rejects his notion that the "new" suburbia has a catalytic function when it comes to "new equality between the sexes". The example of Edge Cities also reveals on which socio-political understandings the concept of Postmetropolis rests. Although those normative foundations (as well as an often present ironic undertone) are never theoretically discussed or even reasoned for (e.g., in the context of critical theory or a postmodern cognitive attitude) but treated as if there were no alternative options, Soja's debate is one that contrasts pleasantly to the ostensible and often also simplistic argumentation patterns of "new-wave boosters" and "spin doctors".
This debate also points to the possibility or even necessity to include other theory offers (e.g., modernization theories) when conceptually positioning certain societal development trends (e.g., an increase in female labor participation and with that the changes in spatially effective gender relations). Social sciences in general and geography in particular draw their analytical power precisely not from the restriction, but rather from a multi-perspective conceptual positioning of their study objects.

Disruptions in Imaging the "Urban"
Based on what we have been discussing so far it has become clear that concepts of the "urban" are in a profound transition process. The image of the city is being shaped by increasingly fragmented urban societies and urban structures, and an increase in the complexity of economic, social, socio-cultural, and spatial structural change patterns. These tendencies in urban development have also been labeled as heteropolis. According to Häußermann [85], the "integration engine (European) city" (translated by the authors) of the industrial age (i.e., the "first modern age" in Beck's terminology) is turning into a place of fragmentation that eventually may lead to the disintegration of the city as a social entity. He attributes these fragmentation processes to the mounting de-localization of economic relations and a progressively economic and socio-spatial decoupling of parts of the urban society.
The image of the postmodern city, however, is not only characterized by fragmentation and disintegration but also by the creation of artificial urban environments that deliberately refrain from making reference to the respective places. So-called Urban Entertainment Centers are the spearheads of these developments. They are staged places of entertainment that break with the (European) idea of historically grown cities and instead create a simulation of a city. Several functions are united there (shopping, entertainment, and recreation) and they offer an environment that is free of the everyday problems from urban life, thus allowing for undisturbed recreational activities.
From a European perspective, postmodern tendencies in urban development therefore also threaten societal developments that could lead to the erosion of traditional European cities and to them losing their authenticity, social balance, integration capability, and (democratic) planning and control of urban development.

Postmetropolis-A Critical Appraisal
The conceptualizations of urban development discussed here are neither immune to criticism nor do they represent exclusive or unrivaled interpretations. What all of the theory offers have in common, be they Soja's comprehensive analysis in Postmetropolis or other research studying postmodern interpretations of social changes and their spatial implications, is that none of them can claim universal validity. This is especially true when, as is the case in Postmetropolis, different theoretical interpretations are merged.
When concentrating on the question of governability of urban developments on the local level, Tai [86] rejects the thesis-formulated as part of the globalization debate-that government actors are losing influence to transnational companies that are becoming more and more powerful. She researched that thesis in her study on Singapore, Hong Kong, and Taipei and argues that, although urban development is dependent on trends in global markets, this does not prejudge forms of political regulation at the local level. Van der Heiden and Terhorst [87] also qualify homogenizing assumptions made in the globalization debate. The authors attempt to conceptualize the considerable development differences in three select European cities (Zurich, Rotterdam, and Manchester) by modifying the variety of capitalism approach towards a variety of glocalization approach. They are convinced that "(t)he strategy a city follows within its international economic activities can be explained by both the specific market conditions a city faces and the role of the national state within the specific form of urban capitalism. This variety of glocalisation trajectories explains the persistent and astonishing differences within the international economic strategies of European cities" [87] (p. 353).
When concentrating on the rising architectural Esperanto as a typical feature of Global Cities and cities that strive to reach that status, Knox and Pain [88] elaborate that, although the architecture's observable homogenization in cities is a very powerful trend, the trend is faced with "resistance". For instance, the persistence of built environments and the "waywardness" of local political decision-making processes on which they note: "tendencies toward homogenization are invariably met with counter-trends" [88] (p. 426). On the other hand, the authors stress that "(w)hat we doubt is that these counter-trends are powerful enough to balance out the homogenizing tendencies in urban development" [88] (p. 426).
The widely discussed phenomenon of suburbanization also contains a large bandwidth of different societal trends when analyzed from a global perspective. While suburbanization in capitalist economies for the most part of the 20th century was mainly carried by (white, hetero-normative) middle-class households, in Latin America, lower social classes contributed substantially to suburbanization developments [89]. The situation in transformation countries is similar: suburbanization and "de-suburbanization" phenomena are carried especially by the poor population and as such are an expression or element of (spatial) adaptation or "weathering" strategies during times of crisis. Furthermore, in capitalist economies, the phenomenon of suburbia, as described above, is subjected to far reaching processes of change. Especially in view of the socio-cultural, socio-economic, and socio-structural changes in the entire urban region and thus also in its peripheral areas, it has become clear that a categorical distinction between core city and suburbia is no longer tenable-if it ever had been. This then leads to the question whether the (spatial) category suburbia is still suited for being scientifically analyzed. We come back to this question in Section 4.3.
What has become evident from these few examples is that the theoretical reasons given in this article for the recent trends in urban development in capitalist economies cannot be generalized when addressing developments in other parts of the world [90]. Especially in connection with the discussion on urban development in the Global South and when considering the debate on the growing importance of cultural differences on a global scale, the question arises whether the six discourses on postmodern urban development, as elaborated on by Soja, can be applied in other parts of the world.
Those thoughts do not even generally apply to capitalist economies in the Global North but instead are focused on certain spaces in North America, especially those that are at the analysis' center of attention [91].
Given the complexity of urban developments and the heterogeneity and variety of theoretical offers that Soja discusses in order to conceptually connect empirical descriptions and theoretical abstractions, it does not come as a surprise that his works received critical reception. The critical debate carried out here is a reminder that each theorization of the urban must reduce complexity and that their epistemological value in the first instance is heuristic in nature. Hence, they offer starting points or "search-lights" for empirical studies. As such the "generalizable particularities" of Los Angeles, as detected by Soja [7] (p. 154), can be understood as starting points when analyzing other "cityspaces".

Conclusions
In this contribution, we view urban development "from the edge" by moving suburbia to the center. We deal with current German and English language contributions on suburbia in the context of a wider debate on urban developments anchored in various different discourses. Thereby, several things become evident.

Suburbia as a Special Place
Suburbia is a special place in a city (region) insofar as it is connected to numerous expectations, wishes, imaginaries, and social practices. The symbolic meaning of suburbia in particular refers to the special role that people associate with certain spaces. Furthermore, suburbia is a dynamic construct that can feature large differences in and between societies, e.g., in connection to the just mentioned imaginaries, wishes, and societal practices those special places are attributed with. An example for this can be found in the American context of the participation and role of different ethnic groups in suburbanization processes. As the discussion has shown, suburbia is no longer a place of (privileged) white, hetero-normative middle-class families but also a place of ethnic differences. In reference to the larger Los Angeles area, Soja [7] (p. 287) discusses an "ethnic quilt" that is spread out over the city. As lively as the debate on the role and meaning of suburbia's ethnic composition in the US is, in Germany, it hardly has any meaning. Whether these different discursive practices are the result of different societal developments or instead point to different discourse cultures cannot be settled here. The comparison to the American situation, however, clearly shows that elaborating on the meaning of ethnical/cultural differences for suburbanization processes in German-speaking contexts is of little relevance. It would therefore be desirable if future research was to close this gap.
The dynamic of suburbia's development always also reflects general societal and urban development processes. Those are never unconditional but always also an expression of earlier developments ("path dependency"). From the perspective of regulation theory, for instance, one can argue that the economic structural breaks in the second half of the 20th century in capitalist economies were not linear and that they did not develop following one particular pattern. Instead, they developed on the basis of specific local/regional contexts in which the globalization forces were adapted to specific local and regional contexts. Thus, it has become clear that post-Fordist urban and regional development does not follow one path but that there are numerous development paths. Since there are no historic "laws" or blue prints that urban and regional developments follow, urban developments are principally open-ended. This reasoning might be unsatisfactory for those who turn to "best practice" examples to legitimize their decisions. On the other hand, it is highly beneficial as it questions the "inevitability" of societal developments (as part of globalization) and allows for considering development options. Of course, those thoughts also pertain to the different urban subspaces (e.g., suburbia) since their developments not only reflect the dynamics of city-wide processes and overarching societal processes but also their specific, locally bound material, cultural, and social resources. By taking those specifics into consideration from a dynamic perspective, suburbia cannot only be depicted in the sense of a snapshot but it can be adequately understood in its spatial and temporal development [11].

Research Desiderata
Additionally, other research desiderata need to be addressed. Other topics, especially those referring back to socio-structural and socio-economic changes, have received little attention in the (German-speaking) debate: differentiation and hybridization of lifestyles [38] (and in this context the competition hetero-normative small families find themselves in with other forms of socialization), changes in household structures (e.g., an increase in childless double income households) [39], the relevance of retirement migration (which also points to relevance of real-estate), and the important role poorer population groups play in the American debate (see [7]). This list is by no means complete. What it does show, however, is how large and thematically differentiated the need for research on suburbia is.
We would like to point to two more fruitful scientific research areas. First, it would lend itself to focus from an international perspective on the different terms and the deviant meanings that are used for spaces beyond core cities. For the French case, for instance, one could address the very different ideas on suburbia by turning to the term Banlieues and with them the topic of social deviance in suburbs. "'Banlieues' have become the symbol of a bleak urban environment, deviant youth, and segregated minorities, whereas 'suburb' in the United States designates quiet, wealthy areas, with nice, large houses and white middle-or upper-class families" [92] (p. 2). Section, as shown by the discussion in Section 2.1, pauperization processes in suburbia could be researched in more detail. These processes are the result of poorer population moving into suburbia (especially in the Global South but not only there) as well as, in part, by the abrupt socio-economic status change of middle-class households due to economic structural breaks (see also Section 2.1).

The End of Suburbia?
As we have seen, suburbia can be understood not only as an empirical phenomenon but also as a discursive concept through which societal complexity can be reduced and be made more accessible. However, both the empirical findings as well as the debates on suburbia show a high level of heterogeneity and diversity, and this has led Short [30] (p. 340), for instance, to argue for the end of suburbia as a phenomenon and as a (useful) discursive instrument. Hence, there is the question of whether the concept of suburbanization continues to adequately reflect current urban regional processes. Frank [24] (p. 8) calls for a radical departure from a spatial understanding of "urbanism" and "suburbanism" instead focusing on "ways of life". Those concepts are not limited to particular places but they open the possibility to reach a more adequate understanding of the fragmented nature of today's metropolitan regions as a patchwork of places. Short [24] (p. 340) also reaches a rather radical conclusion that points to the necessity "to build more sophisticated models and understandings of a complex metropolis without the crutch of these increasingly obsolete terms". From our point of view, this does not result in suburbia's end (especially not as a discursive instrument) but it does result in the necessity to a conceptual reorientation and/or extending the urban development debate.

Regional Urbanization as an Ambitious Concept for Understanding Urban Regional Developments
For many decades, a form of urban development dominated capitalist societies, which Soja termed Metropolitan Urbanization. Its main feature is the clear-cut dichotomy between cities and suburbs (see list according to Huq in Section 1.2). (Core) Cities, on the one hand, generated heterogeneous cultures, numerous types of social interaction forms as well as a high level of creative potential, but also crime, drugs, corruption, and other "vices". Suburbia, on the other hand, is characterized by homogeneous lifestyles and ways of life [1] (p. 1). These differences between center and periphery, however, have become more and more obsolete in the course of ever more complex development patterns in urban regions and subsequently the simplified discursive positions associated with them. One of the largest challenges when scientifically analyzing urban development is to appropriately pay tribute to changing societal realties by altering methodological approaches and conceptual frames accordingly. To us, Soja's concept of Regional Urbanization, as described in Postmetropolis, allows doing that. Soja stresses the necessity to analyze urban development as complex constructions in which societal trends are connected to one and other and that take place on different scales. Central to Soja's theorization is the interconnectedness of the economy, the social, and the spatial that forms a complex structure of interacting spheres of influence. This complex approach is the guiding thread that runs through all his deliberations. Following a political-economic understanding social changes in the Postmetropolis are always referred to political and economic structures and actors. At the beginning of Chapter 9 (Fractal City), Soja [7] (pp. 264ff.) stresses that social structures in the globalized post-Fordist Exopolis have become more and more complex and fluid and that they break with traditional understandings of urban developments (see also Section 3.3). He goes on to state that, although traditional socio-spatial polarities have not vanished altogether, they do feature polymorphous traits. Consequently, thoughts on the "dual city" (bourgeoisie and working class dichotomy) or on ethnically segregated cities with black and white dichotomies can contribute to explaining social stratification in Postmetropolis only in a limited way. Soja [7] (p. 265) detects familiar mechanisms as an important driver of newer socio-spatial fragmentations "that inherent in the new urbanization processes has been an intensification of socio-economic inequalities". Soja [7] (p. 242) notes that "(i)n the Era of the Postmetropolis, it becomes increasingly difficult to 'escape from the city' for the urban condition and urbanism as a way of life are becoming virtually ubiquitous. And in the wake of these changes, the ways in which the metropolitan region is patterned by class, race, and gender relations have become more complex and opaque". Soja tries to grasp the increasing complexity of socio-spatial reality by applying a complex political-economic theory. Of course, even such a complex theory offer cannot cover everything that needs to be said about the development of cities in a global context. If one, however, does allege that social sciences are multi-paradigmatic (language) games that analyze their topics from different angles, then Soja's deliberations offer a wide range of possibilities to ambitiously theorize on Postmetropolis' developments.

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