This article proposes general criteria to redefine the city as object of scientific knowledge. Traditional strategy has atomized city study on a myriad of specialized approaches, evading an integral view of its nature and its dynamics. On these notes we proposed an inverse procedure: to define the city as a scientific object with its own characteristics and peculiarities, structured on the basis of a provisional definition of a specific theoretical field, the socio-spatial. The development of this theoretical field has an additional requisite, to use scientific principles proposed by the complexity theory.