While Southern California and the Central Valley added thousands of new residents in 2002-03, four Bay Area counties experienced population declines, with San Francisco losing more than any in the state, according to new census data released today. Stymied by a slowly rebounding economy and saddled with a low birthrate, San Francisco lost 10,301 people from July 1, 2002 to July 1, 2003, by far the most -- both in sheer numbers and percentage-wise -- of the seven counties statewide that saw population losses. Alameda, San Mateo and Marin counties, as well as Santa Cruz County and two others, also...