Geographic information systems, GIS, are a really valuable tool for planning projects. Most GIS applications available from local counties and cities are web-based interactive mapping applications that allow you to search for a property parcel and view key information like property boundaries, topo contour lines, utilities, and aerial photos. All the information is scaled and most aerial photos available are orthogonally corrected (corrected to display to scale and not be distorted by the earth’s curvature).
So what’s the utility of GIS in landscape projects? The information can help with laying out site plans, confirming information on existing plans, siting trees, buildings and other key features. Most of the applications available online are intuitive and easy to use.
Marin Map (all of Marin County)
Napa County GIS
Sonoma County PRMD Active Map (for areas in unincorporated Sonoma County)
City of Petaluma GIS Portal
GIS Article from Wikipedia
Listing of GIS sites from around the State