In a literal geographic sense, yes, but as someone who has lived in the Los Angeles area for 32 years, I can categorically state that San Francisco is considered by Californians to be in Northern California.
Although there is no official demarcation line between the northern and southern parts of the state, the general interpretation is that you draw a line across the top of San Luis Obispo, Kern and San Bernardino counties from the Pacific to the state's eastern border. Everything north of that line is considered NoCal.
Many people don't draw lines on maps, but go only by counties. Looked at this way, Southern California includes the 42,383 square miles encompassed by Los Angeles, San Diego, Orange, San Bernardino, Riverside, Ventura, Imperial, and Santa Barbara counties. As of January 2007, the estimated population of these counties was 21,586,151.
The vast San Joaquin Valley runs from just north of the Tehachipi Mountains (about 70 miles north of L.A.) all the way up the central part of the state. When Californias talk about central California, that's usually what they mean. It can be clearly seen in this topographical view of the state, as can the San Francisco bay area. You can clearly see that, even if one were to cut the state literally in half, San Francisco would still be north of the literal midpoint.
