Urban spaces that enable diversity and make it possible to experience it help to acquire social skills, which are an important prerequisite for socialisation processes and mental health.
By practising urban diversity, the foundations are laid for productive dealing with social differences and with conflicts.

The demand for diversity can not only be applied to the formation of heterogeneous urban spaces, it is also a fundamental right based on the General Equal Treatment Act (Allgemeines Gleichbehandlungsgesetz – AGG) of the German Constitution. Accordingly, “Everyone has the right to free development of his or her personality insofar as he or she does not violate the rights of others” (Art. 2, para. 1). The Equal Treatment Act stipulates that no one shall be disadvantaged or excluded on grounds of race or ethnic origin, sex, religion or belief, disability, age or sexual identity.
In this sense, diversity in the urban public sphere must be regarded both from the perspective of the design and the social character of urban spaces. A diverse urban landscape inevitably has an impact on the development of social diversity. The implementation of an “open city” that not only makes social heterogeneity possible but also promotes it, depends, however, on many other factors. Social behaviour, belonging to a specific milieu, cultural practices and income or class have a major influence on the way diversity is practised.
The question to be answered is how diversity can be lived and which urban planning and socio-psychological insights are helpful. In the 1950s, American psychologist G.W. Allport postulated the so-called contact hypothesis, which says that contact can reduce prejudices (Allport, 1954). For his hypotheses, Allport proposed four key factors that enable contact across groups: an equal status in the situation, common goals, cooperation and support by an official authority (ibid.). These socio-psychological factors can and should serve as orientation points for urban development and planning.

In addition to numerous other factors, a diverse urban landscape has an impact on the development of social diversity, the implementation of an "open city" and not least on the social skills of its inhabitants.

While the diversity of urban lifestyles and social milieus is regarded as a basic prerequisite for a lively urban environment, the current development of cities shows a clear tendency towards homogenisation of districts and neighbourhoods. Gentrification and segregation – i.e. the displacement of specific population groups – do not only lead to an unequal distribution of urban resources. Fragmentation into homogeneous urban quarters also impairs the dynamics of the city as an open system. The potentially polarising effects of ethnic diversity on social cohesion have been discussed in recent decades (Putnam, 2000, 2007). On the one hand, studies show that a high degree of heterogeneity correlates negatively with trust (Stolle et al., 2008). At the same time, it has been shown that social contact can create trust as well as reduce distrust in different situations and groups (Pettigrew and Tropp, 2006; Stolle et al., 2006). Paolini et al. attribute this to the reduction of anxiety mediated through social contact (Paolini et al., 2004). Social psychology studies focusing on contact and group relationships suggest that the connection between contacts within different communities can even promote the development of an overarching identity (Pettigrew and Tropp, 2008). Thus, the city is a source of friction that allows different groups to articulate themselves. The contradictions and asymmetries are also what make a functioning urban diversity so resilient.
Diversity is therefore not a harmonious state that is naturally created, but a demand that must be actively implemented. The implementation of diversity in urban areas can be regarded as a basic prerequisite for an open civil society.

The lack of cultural and social diversity can lead to a deficit of social skills, which in turn leads to social isolation and conflicts in the city.

1. Allport, G.W., 1954. The nature of prejudic. Addison-Wesley, Cambridge, MA.
2. Paolini, S., Hewstone, M., Cairns, E., Voci, A., 2004. Effects of direct and indirect cross-group friendships on judgments of Catholics and Protestants in Northern Ireland: The mediating role of an anxiety-reduction mechanism. Personality and Social Psychology Bulletin 30, 770-786.
3. Pettigrew, T.F., Tropp, L.R., 2006. A meta-analytic test of intergroup contact theory. Journal of Personality and Social Psychology, 90, 751-783.
4. Pettigrew, T.F., Tropp, L.R., 2008. How does intergroup contact reduce prejudice? Meta-analytic tests of three mediators. European Journal of Social Psychology 38, 922-934.
5. Putnam, R.D., 2007. E Pluribus Unum: Diversity and community in the Twenty-first century. The 2006 Johan Skytte Prize Lecture. Scandinavian Political Studies 30, 137-174.