The Government Information Center has a wide variety of government publications with statistics for San Francisco. Contact the GIC for assistance in locating statistics.
The official and most thorough population survey is conducted by the U.S. Census Bureau and is called the Decennial Census (as it is conducted every 10 years, most recently in April 2010). The Decennial Census strives to collect data from every household in the U.S. and its territories. Statistics that are gathered after the Decennial Census has been completed (between decades), including data gathered by the Census Bureau, are estimates and projections based on surveying a sample population, with the previous Decennial Census data usually used as a baseline.
Since San Francisco is a combined City and County, statistics that are gathered at the county level also apply to San Francisco's city boundaries, such as U.S. Census Bureau data and demographic information from the California Department of Finance.
San Francisco is also a Metropolitan Statistical Area (MSA) that includes other counties. The cities and counties included in a statistical area depend on the government agency's source and/or geographical definitions for the statistics gathered. Always check the geography of the San Francisco statistic's source.