Niterói is a municipality of the state of Rio de Janeiro in the southeast region of Brazil. It lies across Guanabara Bay facing the city of Rio de Janeiro and forms part of the Rio de Janeiro Metropolitan Area. It was the state capital, as marked by its golden mural crown, from 1834 to 1894 and again from 1903 to 1975. It has an estimated population of 511,786 inhabitants (2018) and an area of 129.375 km2, making it the fifth most populous city in the state. It has the highest Human Development Index of the state and the seventh largest among Brazil's municipalities in 2010. Individually, it is the second municipality with the highest average monthly household income per capita in Brazil and appears in 13th place among the municipalities of the country according to social indicators related to education. The city has the nicknames of Nikity, Nicki City and the Smile City (Cidade Sorriso).