Utilize the input text as a context reference, choose the right relationship between Turkish Airlines and Istanbul from the options. Options: product/material produced, manufacturer, distributed by, industry, position held, original broadcaster, owned by, founded by, distribution format, headquarters location, stock exchange, currency, parent organization, chief executive officer, director/manager, owner of, operator, member of, employer, chairperson, platform, subsidiary, legal form, publisher, developer, brand, business division, location of formation, creator.

Partnerships with airlines including Lufthansa and Poland’s LOT remain key even as Turkish Airlines builds its Istanbul base into a global hub with an eye to the success of Gulf operators Dubai-Emirates, Qatar Airways Ltd. and Abu Dhabi’s Etihad Airways PJCS, Kotil said.

Answer: location_of_formation