Recently more cities and counties in California have established or improved their online GIS mapping Web sites. Search on the Merced County site for real properties by address or parcel number. The parcel map displays the nearby properties and their addresses. A detailed profile gives property characteristics with valuations.
The City of Modesto (view in Internet Explorer only) map isn’t straight forward but has many useful features, once you learn how to use them. Plot geographical features, government buildings, parcels and businesses by description, SIC code, address or APN and delineate these within an adjustable radius. Print or copy maps into other applications.
The San Joaquin County parcel viewer is streamlined and easy to use. Search by parcel number, street address or partial street name to get a list of all properties with those characteristics. Select a property and it appears on a parcel map showing all other nearby parcels. Somewhat limited aerial photos are available from 1994-2006.
Some of the other California counties with interactive GIS property mapping are listed at this site.
In Nassau county, NY, we have a similar and sometimes very valuable data base.
A few years back, the county hired a private firm to re-assess all properties in the county. At the close of that daunting task, each and every property in the county was listed in a searchable data base along with all information such as lot and block etc, and the assessed value. It even displays a photo of the property at the time it was assessed.