Istanbul (Turkish: İstanbul, historically also known as Byzantium and Constantinople; see the names of Istanbul) is the largest city in Turkey and fifth largest city proper in the world with a population of 12.6 million. Istanbul is also a megacity, as well as the cultural and financial centre of Turkey. The city covers 39 districts of the Istanbul province. It is located on the Bosphorus Strait and encompasses the natural harbour known as the Golden Horn, in the northwest of the country. It extends both on the European (Thrace) and on the Asian (Anatolia) sides of the Bosphorus, and is thereby the only metropolis in the world that is situated on two continents.
In its long history, Istanbul has served as the capital city of the Roman Empire (330–395), the Eastern Roman (Byzantine) Empire (395–1204 and 1261–1453), the Latin Empire (1204–1261), and the Ottoman Empire (1453–1922). The city was chosen as joint European Capital of Culture for 2010. The historic areas of Istanbul were added to the UNESCO World Heritage List in 1985.
Istanbul has a temperate climate but is located within a climatic transition zone  between oceanic and Mediterranean climates. In summer the weather in Istanbul is hot and humid, the temperature between June and September averaging 28 °C (82 °F). During winter it is cold, wet and often snowy, averaging 5 °C (41 °F). The humidity of the city is constantly high which makes the air feel much harsher than the actual temperatures. The city being located in the second most humid region of the country, has an average annual humidity of 79%. Average annual precipitation is 693 mm (27 in). Summer is the driest season. Snowfall is quite common between the months of December and March, snowing for a week or two, but it can be heavy once it snows. The city is also quite windy, having an average wind speed of 17 km/h (11 mph).