Claim: Rio de Janeiro is a metropolis.

Greater Rio de Janeiro , officially Rio de Janeiro Metropolitan Region -LRB- Grande Rio , officially Região Metropolitana do Rio de Janeiro , in Portuguese -RRB- is a large metropolitan area located in Rio de Janeiro state in Brazil , the second largest in Brazil and third largest in South America . It consists of 21 municipalities , including the capital of the State , Rio de Janeiro .   The metropolitan area of Rio de Janeiro is known as a historical , cultural and economic centre of Brazil , with a total population of 12.6 million inhabitants . The region was first officially defined on July 1 , 1974 , less than 1 year till 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 . It was changed several times to include or remove different cities in different moments of the history , in the years 1993 , 2001 , 2002 , 2009 and 2013 .   The water supply plans of the region are coordinated , and transportation in the area is heavily interconnected with urban intermunicipal buses to all municipalities in the area , trains over the capital to some Baixada Fluminense municipalities , ferry boats to some of the Guanabara Bay municipalities and major inter-city freeways such as the Rio -- Niterói Bridge , Red Line , President Dutra freeway and Niterói-Manilha freeway . Most transportation methods are integrated with the capital inner-transportation system of buses , trains , metro , freeways and expressways .