For the State of California, locating a main State GIS data node is relatively simple... enter California Spatial Information Library (CASIL). For direct access to data, see the "data Collections" link (left side-bar) and browse the frequently collected datasets category where you'll find access to admin layers (parks, water districts etc...), cultural data layers (census data), imagery, physical data products and much more. Perhaps of greatest interest is the imagery - Digital Orthophoto Quadrangle GeoTiff (DOQQ), SPOT imagery and much more.
DOQs
For DOQs and other imagery data products, these data are available directly from: http://casil.ucdavis.edu/casil/remote_sensing/doq/
To access the catalog homepage go to http://gis.ca.gov/data.epl
DRGs
For information and downloads of California State DRGs see http://gis.ca.gov/casil/gis.ca.gov/drg/ or http://drg.casil.ucdavis.edu/The maps are organized into 1x1 degree blocks covering the state of California. The source maps for DRGs were georeferenced to the UTM grid, but DRG images for California are available in Albers equal area projection (see the projection information). A DRG is useful as a source or background layer in a GIS, as a means to perform quality assurance on other digital products, and as a source for the collection and revision of DLG data. Available as 7.5 minute, 30x60 minute, and 1x1 degree blocks
California Spatial Information Library (CASIL). Most data are maintained in an Albers projectionCalifornia Spatial Information Library - CaSIL Home http://gis.ca.gov/
DEMs
And here's a total score if you need 7.5 minute Digital Elevation Models for California
1:24,000-scale quadrangles can be access via http://130.166.124.2/ca_index.html
or view these data using a map UI
http://130.166.124.2/ca_dems.2/clickable/overview.htm
LANDSAT
For Landsat 7 imagery data products you can access these data at http://casil.ucdavis.edu/casil/remote_sensing/landsat/landsat7/calview/
In addition to providing a vast amount of geospatial data products, CASIL is also hosting several fine webmapping services. These include:
- CaSIL GeoFinder - GeoFinder is a tool that helps find and retrieve geographic and environmental data from the California Resources Agency
- DRG Mapsurfer This site provides an interface for downloading USGS DRGs for California. Also has the capability to display DOQQs as well as Landsat color composites to enhance the browsing experience.
- The California Digital Conservation Atlas is a comprehensive public website for conservation information.
Another fine bookmark for California GIS data is the State Geospatial Information Office Homepage - http://gio.resources.ca.gov/
Other California Data Links of interest:
- California Vegetation Map Catalog
- California Department of Fish and Game Data Site
- San Francisco Bay Area Regional Database (BARD) with 1:24,000
DEMs , DLGs , DRGs , DOQs - U.S. Fish And Wildlife Service Data for California
- Caltrans GIS Data Library
- California Gap Analysis Project: Statewide Datasets
- California Statewide database from UC Berkeley
- A comprehensive guide to California State webmapping resources