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How to Read an Assessor Parcel Number (APN) and Plat Map

A practical guide to understanding how county tax assessors identify real property and track land boundaries.

What is an Assessor's Parcel Number (APN)?

An Assessor's Parcel Number (often abbreviated as APN, PIN, or Folio Number) is a unique identifier assigned by your local county tax assessor to a specific parcel of real estate. While street addresses can change when municipal post offices rename streets or adjust building numbers, an APN remains directly tied to the county deed books and cadastral mapping system.

How Most County APNs Are Structured (Book, Page, Parcel)

While formatting varies across states, most US counties organize parcel numbers hierarchically. An APN like 123-45-678 or 15 30 32 61056 001 0470 typically breaks down into three key geographic tiers:

Book Number (The First Section): Represents the specific cadastral map volume kept in the county assessor's office. This volume covers a broad geographic section or district within the county.
Page or Block Number (The Middle Section): Refers to a specific double-page spread or neighborhood block within that volume. It zooms in to a subdivision, survey tract, or street cluster.
Parcel or Lot Number (The Final Section): Identifies the individual lot of land on that page. In some counties, a final digit or suffix indicates whether the parcel was split or subdivided from an original tract.

APN vs. Street Address vs. Legal Description

Homeowners often confuse these three identifiers, but they serve completely different legal and administrative purposes:

Identifier	Primary Purpose	Who Controls It
Street Address	Postal delivery, emergency services (911), and navigation.	US Postal Service & City Planning
Parcel Number (APN)	Tax assessment, property valuations, and property tax billing.	County Property Appraiser / Assessor
Legal Description	The binding legal definition that transfers property ownership in deeds.	Recorded County Deed & Title Registry

How to Read a County Plat Map

A plat map is a drawn-to-scale surveyor document recorded in the county courthouse showing the boundary lines, easements, and public streets of a subdivision or tract. When reviewing a plat map for your home, look for these four core elements:

Lot Dimensions: Small numbers printed along the perimeter lines of each parcel show the exact length of the boundary in feet (e.g., 75.00' along the street frontage and 120.00' along the side lot lines).
Easements (P.U.E. or D.E.): Dashed lines running inside your lot lines typically designate a Public Utility Easement (P.U.E.) or Drainage Easement (D.E.). These areas belong to you, but power companies, water utilities, or city crews hold the legal right to access them and you generally cannot build permanent structures over them.
Setback Lines: Dotted lines indicating how many feet any house or garage must be set back from the street or neighboring property lines under local zoning rules.
Right-of-Way (R/W): The land dedicated for public roads and sidewalks. Your property line usually begins several feet behind the street curb, not right at the pavement edge.