A county assessor's office keeps a set of maps to identify the location of every parcel of land in a county. The maps are usually accessible in old bound volumes and on computer terminals using geographic information system software.
If you don’t know the address of a piece of property, such as a vacant lot, you can use the maps to find a parcel map for the piece of property, and from that its address or its assessor’s parcel number.
You then use the address or parcel number to determine the assessed value and owner of the property.
At the assessor's office there are maps that divide the county into geographic areas, each of which corresponds to a large bound book, called a map book.
Use the maps to find the map book for the area within which the property you are researching is located.
At the beginning of each map book will be a map that shows the various blocks (like city blocks) within the geographic area the map book covers.
Go to the page for the block that has the property you’re researching.
On the block page you’ll find a map that shows all the individual lots or parcels of property on that block.
Each lot will show its street address or its assessor's parcel number.
You then can use the assessor's parcel number index or address index to check for ownership and assessed value of the parcel.
Sample Block and Parcel Map
To see what block and parcel maps look like, go to the Alameda County Assessor's Office online database for
Type a street address into the search boxes, such as:
2180 Milvia Street, Berkeley
(which is the address for Berkeley City Hall)
At the new page, click on the Map link to get a pdf file of the block and parcel map for this address.
Geographic Information Systems
Some counties are using Geographic Information System software to let you search for the parcel number or address of a property using computer generated maps. These maps are similar to the map book, block and lot/parcel maps of old.
One example of a GIS map is at the Contra Costa County Assessor's Office:
At that page select the zoom tool (the magnifying glass icon with a + on it) above the map and then click anywhere on the map to zoom in. Continue clicking until you see a number displayed for a parcel of property.
This is the street address for that property. You now can click on the select tool (just to the right of the zoom tools) and then click on the street address number to display information about the property to the right, such as the assessor parcel number for the property.