Istanbul also İstanbul, formerly known as Byzantium and Constantinople, is the most populous city in Turkey and the country’s economic, cultural and historic center. Istanbul is a transcontinental city in Eurasia, straddling the Bosporus strait (which separates Europe and Asia) between the Sea of Marmara and the Black Sea.
Its commercial and historical center lies on the European side and about a third of its population lives in suburbs on the Asian side of the Bosporus. With a total population of around fifteen million residents in its metropolitan area, Istanbul is one of the world’s largest cities by population, ranking as the world’s fifteenth-largest city and the largest city in Europe.
The city is the administrative centre of the Istanbul Metropolitan Municipality (coterminous with Istanbul Province).
The city held the strategic position between the Black Sea and the Mediterranean. It was also on the historic Silk Road. It controlled rail networks between the Balkans and the Middle East and was the only sea route between the Black Sea and the Mediterranean. In 1923, after the Turkish War of Independence, Ankara was chosen as the new Turkish capital, and the city’s name was changed to Istanbul. Nevertheless, the city maintained its prominence in geopolitical and cultural affairs.
The population of the city has increased tenfold since the 1950s, as migrants from across Anatolia have moved in and city limits have expanded to accommodate them. Arts, music, film, and cultural festivals were established towards the end of the 20th century and continue to be hosted by the city today. Infrastructure improvements have produced a complex transportation network in the city.
Over 12 million foreign visitors came to Istanbul in 2015, five years after it was named a European Capital of Culture, making the city the world’s fifth-most popular tourist destination. The city’s biggest attraction is its historic center, partially listed as a UNESCO World Heritage Site, and its cultural and entertainment hub is across the city’s natural harbor, the Golden Horn, in the Beyoğlu district. Considered a global city.
It hosts the headquarters of many Turkish companies and media outlets and accounts for more than a quarter of the country’s gross domestic product. Hoping to capitalize on its revitalization and rapid expansion, Istanbul has bid for the Summer Olympics five times in twenty years.
In the Köppen–Geiger classification system, Istanbul has a borderline Mediterranean climate (Csa), humid subtropical climate (Cfa) and oceanic climate (Cfb), due to its location in a transitional climatic zone. Since precipitation in summer months ranges from 20 to 65 mm (1 to 3 in), depending on location, the city cannot be classified as solely Mediterranean or humid subtropical.
Istanbul’s persistently high humidity reaches 80 percent most mornings. Because of this, fog is very common, although more so in northern parts of the city and away from the city center. Dense fog disrupts transportation in the region, including on the Bosphorus, and is common during the autumn and winter months when the humidity remains high into the afternoon.The humid conditions and the fog tend to dissipate by midday during the summer months, but the lingering humidity exacerbates the moderately high summer temperatures.
During these summer months, high temperatures average around 29 °C (84 °F) and rainfall is uncommon; there are only about fifteen days with measurable precipitation between June and August. The summer months also have the highest concentration of thunderstorms.
Winter is colder in Istanbul than in most other cities around the Mediterranean Basin, with low temperatures averaging 1–4 °C (34–39 °F). Lake-effect snow from the Black Sea is common, although difficult to forecast, with the potential to be heavy and—as with the fog—disruptive to the city’s infrastructure.Spring and autumn are mild, but often wet and unpredictable; chilly winds from the northwest and warm gusts from the south—sometimes in the same day—tend to cause fluctuations in temperature.
Weather is mixed in the area. Istanbul has an annual average of 130 days with significant precipitation, which amounts to 810 millimeters (31.9 in) per year. The highest and lowest temperatures ever recorded in the city center on the Marmara coast are 40.5 °C (105 °F) and −16.1 °C (3 °F). The greatest rainfall recorded in a day is 227 millimeters (8.9 in), and the highest recorded snow cover is 80 centimeters (31 in).
Global warming in Turkey may cause more urban heatwaves, droughts, storms, and flooding. Sea level rise is forecast to affect city infrastructure, for example Kadıkoy metro station is threatened with flooding. Xeriscaping of green spaces has been suggested, and Istanbul has a climate-change action plan.
During the Ottoman period, Üsküdar (then Scutari) and Kadıköy were outside the scope of the urban area, serving as tranquil outposts with seaside yalıs and gardens. But in the second half of the 20th century, the Asian side experienced major urban growth; the late development of this part of the city led to better infrastructure and tidier urban planning when compared with most other residential areas in the city.
Much of the Asian side of the Bosphorus functions as a suburb of the economic and commercial centers in European Istanbul, accounting for a third of the city’s population but only a quarter of its employment.
As a result of Istanbul’s exponential growth in the 20th century, a significant portion of the city is composed of gecekondus (literally “built overnight”), referring to illegally constructed squatter buildings. At present, some gecekondu areas are being gradually demolished and replaced by modern mass-housing compounds.
Moreover, large scale gentrification and urban renewal projects have been taking place, such as the one in Tarlabaşı;some of these projects, like the one in Sulukule, have faced criticism.The Turkish government also has ambitious plans for an expansion of the city west and northwards on the European side in conjunction with plans for a third airport; the new parts of the city will include four different settlements with specified urban functions, housing 1.5 million people.