A plat map comes with your preliminary title report (provided by your title company with maps from the Santa Clara County tax assessor’s office when you purchase or sell a home in California), tucked away at the back and somewhat mysterious with lots of numbers in small print. It holds quite a bit of helpful information if you know what it is you’re seeing. Today we’ll view a sample of one of these – breaking down the plat map shown as a small thumbnail image on the right to more readable parts so that you can learn how to “read” or understand a plat map.

Quick overview of what’s on a plat map

There’s a wealth of information on the plat map. Take a look and see what you can pick out on your own first.



Plat Map of part of the Cambrian area of San Jose



You can see on the top and left sides that it’s at the intersection of Camden and Union, and inside you can easily find the street names. On the far left side, you’ll see a tract number and the name “Cambrian Park Estates”, which is the name of the subdivision. Where Bernice and Elaine meet, you can see a line with another perpendicular to it in the road – that’s where the surveyor’s mark or survey marker may be found (if it’s not paved over). See image below of what a survey marker looks like (there’s some variation). This is one of the items used in determining locations such as property bounds.



Photo of a survey marker or surveyor's mark


The top part of the plat map page also has something that looks a bit like the arrow on a compass which provides the orientation of the properties (north/south/east/west) – see below.  That directional info is now readily find-able online, but this used to be the easiest way (and most accurate) to answer the question “which way does the home face?” Look at the map, find the parcel and you’ll know its orientation.



Plat map showing orientation or direction



Let’s look a little closer at the individual parcel or small cluster of parcels level, below. I’ve edited this part of the first plat map image to indicate which numbers are which.

  • the number in the street, such as 3371 or 3353, is the house or building number
  • the underlined number is the parcel number (every property has an Assessor’s Parcel Number, and this is that last part of that number)
  • the number in the middle which is not underlined is the lot number
  • the other numbers represent the measurements of the lot



Plat map elements explained



Calculating the parcel dimensions

How can you tell the lot dimensions or how big the lot is? For the lines between the parcels, perpendicular to the street, if all of them are the same distance, only one will be listed. For example, please look at the line between lots 13 and 14, or lots 11 and 12, where there’s a “96” listed. That is the distance from the front to the back of the parcel – and all of the others shown.

The frontage is 62 feet in most cases on this map. If we look at lot 14, we can see that the lot dimensions are 62 feet by 96 feet, or 5952 square feet. It gets trickier when the lots have odd angles, and there are programs to help calculate that area.

How is the plat map useful to you?

Can this information be really useful to you? You bet it can.  Sometimes we see homes for sale in which the lot size is said to be a certain amount, say 6000 SF, but having seen the yard, it appears much, much larger (or smaller). By studying this page, you can check the dimensions and see if the number quoted as the lot size is correct or not.

Several times in my career I have found a lot size to be under-estimated or under-reported in the county records.  This is especially true with irregularly shaped lots (such as pie-shaped lots or lots with many sides to them – more than four).  If a builder primarily subdivided with 6000 SF lots, that number may be inputted to the county records for every parcel, even if the one you’re looking at buying or currently own is much, much more.

I won’t say it’s a fun geometry project, but learning that a home is sitting on a 9000 or 10,000 SF lot rather than 6000 is money in the bank if you’re buying or selling such a home.  Many Realtors will not get the lot measured in person or referencing the plat map, but this extra step is extraordinarily helpful in understanding a home’s true value.   So first we must understand how to read a plat map, then know and act on what we see if there’s anything that does not look correct.

Plat maps are so important that if there’s a small typo in them, the lender for a buyer will not fund the loan until it’s corrected. (I know, it happened to me about 10 years ago on a Willow Glen home I listed and sold on Arata Court.)  When you get the preliminary title report, whether you’re buying or selling, don’t ignore it!  The rest of the contents of the prelim are also important, but for today I want to encourage agents and consumers to take the time to look also at the parcel map at the end of the prelim and see if everything looks correct.  It may save you both time and money to catch any errors upfront.


Further reading:

What is a preliminary title report? Why does it matter?

Where are the easements? Request a color coded easement map from your title company!

What does “et ux” mean in the preliminary title report?

Patio Homes or Zero Lot Line Houses in Silicon Valley