Vienna is the capital and largest city of Austria and one of the nine states of Austria. Vienna is Austrias primary city, with a population of about 1.8 million Vienna is host to many major international organizations, including the United Nations and OPEC. The city is located in the eastern part of Austria and is close to the borders of the Czech Republic, Slovakia, and Hungary. These regions work together in a European Centrope border region. Along with nearby Bratislava, Vienna forms a metropolitan region with 3 million inhabitants. In 2001, the city centre was designated a UNESCO World Heritage Site. Apart from being regarded as the City of Music because of its musical legacy, Vienna is also said to be "The City of Dreams" because it was home to the worlds first psycho-analyst – Sigmund Freud. The citys roots lie in early Celtic and Roman settlements that transformed into a Medieval and Baroque city, and then the capital of the Austro-Hungarian Empire. It is well known for having played an essential role as a leading European music centre, from the great age of Viennese Classicism through the early part of the 20th century. The historic centre of Vienna is rich in architectural ensembles, including Baroque castles and gardens, and the late-19th-century Ringstraße lined with grand buildings, monuments and parks. Vienna is known for its high quality of life. In a 2005 study of 127 world cities, the Economist Intelligence Unit ranked the city first for the worlds most liveable cities. Between 2011 and 2015, Vienna was ranked second, behind Melbourne, Australia. For eight consecutive years, the human-resource-consulting firm Mercer ranked Vienna first in its annual "Quality of Living" survey of hundreds of cities around the world, a title the city still held in 2016. The UN-Habitat has classified Vienna as being the most prosperous city in the world in 2012/2013. The city was ranked 1st globally for its culture of innovation in 2007 and 2008, and sixth globally in the 2014 Innovation Cities Index, which analyzed 162 indicators in covering three areas: culture, infrastructure, and markets. Vienna regularly hosts urban planning conferences and is often used as a case study by urban planners. Between 2005 and 2010, Vienna was the worlds number-one destination for international congresses and conventions. It attracts over 6.8 million tourists a year.