Utilize the input text as a context reference, choose the right relationship between Twitter and SAN FRANCISCO 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.

SAN FRANCISCO - Twitter has lifted its character limit for direct messages between users, saying it would help make the private side of Twitter "more powerful and fun".

Answer: headquarters_location