Geographic Information Systems (GIS)

Geographic Information Systems (GIS) in Napa County

Local agencies in Napa County have added Geographic Information Systems (GIS) to their automation infrastructure. GIS combines graphic representations (maps) with alphanumeric data, such as owner's name and address, property values, number of registered voters, etc. GIS provides the ability to visualize and analyze relationships between geographic locations and information associated with that location. The key to a cost-effective and robust GIS is to share maps, data, maintenance responsibilities and costs between as many agencies as possible.

Base Map

The foundation of a GIS is the base map, which locates major geographic features such as roads, watercourses and jurisdiction boundaries, and ties them to known locations on the earth's surface, which are often determined using satellite or aerial imagery and a global coordinate system. Once the base map is established with as many coordinate points as possible, various layers of spatial information can be built onto the base map. Layers can include assessor parcel boundaries; aerial photographs showing buildings, etc.; soil types; topography (slope) and other natural and human-made features.

What You Can Do With it

When the layers have been added, then staff, and eventually the public, can query the GIS data and receive answers in both maps and tables. For example, one simple function is to highlight a certain parcel on the appropriate map layer and then ask the GIS to return a list of property owners within a certain distance of that parcel. The list can be returned as labels, a printout, a map with all the parcels highlighted or a computer file that can be emailed.

A more complex task that GIS can perform is the redistricting of county supervisorial districts that is mandated every ten years after the census is complete. The GIS program is given the population of the county by census tract. The program then returns one or more scenarios of district boundaries that will result in an equal population per district. Once the preferred option is selected, the program can then be given the boundaries of other entities, such as school districts and municipalities. Using these boundaries, the system can draw preferred precinct boundaries which will meet the legal requirements for maximum number of voters per precinct.

One final example would be to associate the incidence of reported crimes to various types of business, i.e., convenience stores, schools, day-care centers, etc. Such a map could help law enforcement plan patrols and / or alert potential targets to the presence of registered offenders. You can access Napa County's GIS database on our website.

More Information

Should you have any questions please contact Napa County Assessor-Recorder-County Clerk John Tuteur at 707-253-4459 or email John.