 The metropolitan area of Rio de Janeiro is known as a historical, cultural and economic centre of Brazil, with a total population of 13 million inhabitants.The region was first officially defined on July 1, 1974, less than 1 year before the fusion of Guanabara into Rio de Janeiro.Several municipalities show a high level of conurbation, with Rio de Janeiro–Baixada Fluminense and Niterói–São Gonçalo being the most clear examples.