Urbanization is the study of the social,political, and economic relationships in cities, and someone specializing in urban sociology studies those relationships. In some ways, cities can be microcosms of universal human behavior, while in others they provide a unique environment that yields its own brand of human behavior. There is no strict dividing line between rural
and urban; rather, there is a continuum where one bleeds into the other. However, once a geographically concentrated population has reached approximately 100,000 people, it typically behaves like a city regardless of
what its designation might be. Urban development covers infrastructure for
education, health, justice, solid waste, markets, street pavements and cultural heritage protection. These constructions usually form part of specific sector programmed, including capacity building measures. Special attention is also paid to slums of large cities. Rehabilitation and reconstruction comprises in particular social infrastructure following natural disasters or conflicts.