Lisbon is recognised as an alpha-level global city because of its importance in finance, commerce, media, entertainment, arts, international trade, education and tourism. Lisbon is one of two Portuguese cities (alongside Porto) to be recognised as a global city. It is one of the major economic centres on the continent, with a growing financial sector and one of the largest container ports on Europe's Atlantic coast. Additionally, Humberto Delgado Airport served 29 million passengers in 2018, being the busiest airport in Portugal, the 3rd busiest in the Iberian Peninsula and the 20th busiest in Europe. The motorway network and the high-speed rail system of Alfa Pendular links the main cities of Portugal to Lisbon. The city is the 9th-most-visited city in Southern Europe, after Istanbul, Rome, Barcelona, Milan, Athens, Venice, Madrid and Florence with 3,539,400 tourists in 2018. The Lisbon region has a higher GDP PPP per capita than any other region in Portugal. Its GDP amounts to US$96.3 billion and thus $32,434 per capita. The city occupies the 40th place of highest gross earnings in the world. Most of the headquarters of multinational corporations in Portugal are located in the Lisbon area. It is also the political centre of the country, as its seat of government and residence of the head of state.