This polygon shapefile displays Census tracts for the San Francisco Bay Area in California, based on entity boundaries established on January 1, 1990. These data have been clipped to the shoreline for cartographic representation. Census tracts are small, relatively permanent statistical subdivisions of a county (or statistical equivalent of a county), and are defined by local participants as part of t he U.S. Census Bureau's Participant Statistical Areas Program. The U.S. Census Bureau delineated the census tracts in situations where no local participant existed or where local or tribal governments declined to participate. This layer is part of the Bay Area Metropolitan Transportation Commission (MTC) GIS Maps and Data collection.This dataset is intended for researchers, students, and policy makers for reference and mapping purposes, and may be used for basic applications such as viewing, querying, and map output production, or to provide a basemap to support graphical overlays and analysis with other spatial data.