With a PPP-adjusted gross domestic product of US$301.1 billion, Istanbul ranked 29th among the world's urban areas in 2011. Since the mid-1990s, Istanbul's economy has been one of the fastest growing among OECD metro-regions. According to Foreign Policy and the McKinsey Global Institute, Istanbul will register the 14th-highest absolute GDP growth among world cities by 2025, with a nominal increase of US$291.5 billion. Istanbul is responsible for 27 percent of Turkey's GDP, with 20 percent of the country's industrial labor force residing in the city. Its GDP per capita and productivity are greater than their national averages by 70 percent and 50 percent, respectively, owing in part to the focus on high-value-added activities. With its high population and significant contribution to the Turkish economy, Istanbul is responsible for two-fifths of the nation's tax revenue. That includes the taxes of thirty billionaires based in Istanbul, the fifth-highest number among cities around the world. As expected for a city of its size, Istanbul has a diverse industrial economy, producing commodities as varied as olive oil, tobacco, transport vehicles, and electronics. Despite having a focus on high-value-added work, its low-value-added manufacturing sector is substantial, representing just 26 percent of Istanbul's GDP, but four-fifths of the city's total exports. In 2005, companies based in Istanbul produced exports worth $41.4 billion and received imports totaling $69.9 billion; these figures were equivalent to 57 percent and 60 percent, respectively, of the national totals. Istanbul is home to Borsa Istanbul, the sole exchange entity of Turkey, which combined the former Istanbul Stock Exchange, the Istanbul Gold Exchange, and the Derivatives Exchange of Turkey. Former Istanbul Stock Exchange was originally established as the Ottoman Stock Exchange in 1866. During the 19th and early 20th centuries, Bankalar Caddesi (Banks Street) in Galata was the financial center of the Ottoman Empire, where the Ottoman Stock Exchange was located. Bankalar Caddesi continued to be Istanbul's main financial district until the 1990s, when most Turkish banks began moving their headquarters to the modern central business districts of Levent and Maslak. In 1995, the Istanbul Stock Exchange (now Borsa Istanbul) moved to its current building in the İstinye quarter of the Sarıyer district. A new central business district is also under construction in Ataşehir and will host the headquarters of various Turkish banks and financial institutions upon completion. As the only sea route between the oil-rich Black Sea and the Mediterranean, the Bosphorus is one of the busiest waterways in the world; more than 200 million tonnes of oil pass through the strait each year, and the traffic on the Bosphorus is three times that on the Suez Canal. As a result, there have been proposals to build a canal, known as Canal Istanbul, parallel to the strait, on the European side of the city. Istanbul has three major shipping ports—the Port of Haydarpaşa, the Port of Ambarlı, and the Port of Zeytinburnu—as well as several smaller ports and oil terminals along the Bosphorus and the Sea of Marmara. Haydarpaşa, situated at the southeastern end of the Bosphorus, was Istanbul's largest port until the early 2000s. Shifts in operations to Ambarlı since then have left Haydarpaşa running under capacity and with plans to decommission the port. As of 2007, Ambarlı, on the western edge of the urban center, had an annual capacity of 1.5 million TEUs (compared to 354,000 TEUs at Haydarpaşa), making it the fourth-largest cargo terminal in the Mediterranean basin. The Port of Zeytinburnu is advantaged by its proximity to motorways and Atatürk International Airport, and long-term plans for the city call for greater connectivity between all terminals and the road and rail networks. Istanbul is an increasingly popular tourist destination; whereas just 2.4 million foreigners visited the city in 2000, it welcomed 11.6 million foreign tourists in 2012, making it the world's fifth most-visited city. Istanbul is Turkey's second-largest international gateway, after Antalya, receiving a quarter of the nation's foreign tourists. Istanbul's tourist industry is concentrated in the European side, with 90 percent of the city's hotels located there. Low- and mid-range hotels tend to be located on the Sarayburnu, while higher-end hotels are primarily located in the entertainment and financial centers north of the Golden Horn. Istanbul's seventy museums, the most visited of which are the Topkapı Palace Museum and the Hagia Sophia, bring in $30 million in revenue each year. The city's environmental master plan also notes that there are 17 palaces, 64 mosques, and 49 churches of historical significance in Istanbul.