State Sen. Leland Yee will be at the official opening of the San Francisco census office today at 2 p.m. The office, located at 1550 Bryant St., is opening in preparation for a complete count of all city residents in the 2010 census. Done every 10 years, the census helps determine the number of seats the state occupies in the House of Representatives, and how to allocate more than $400 billion of federal funding.