Niterói (Portuguese pronunciation: [niteˈɾɔj]) is a municipality of the state of Rio de Janeiro in the southeast region of Brazil. It lies across Guanabara Bay from the city of Rio de Janeiro and forms part of the Rio de Janeiro Metropolitan Area. It has an estimated population of 487,327 inhabitants (2010) and an area of 129.375 km (80.39 mi), making it the sixth most populous city in the state. It has the highest Human Development Index of the state. The city has the nicknames of Nikity, Nicki City and the Smile City (Cidade Sorriso).