Monday, November 5, 2012

Parcel Identifiers - Standards and Practice

Parcel Identifiers
A Review of Standards and Practice

There are many systems and specifications for parcel identifiers.  Most of these are associated with real estate tax systems but there are also parcel ownership identifiers, real estate improvement identifiers land transaction identifiers, generally on publicly managed lands.  This document reviews some of the recent standards and some best practices for parcel identifiers.


The International Association of Assessing Officers (IAAO) has an established standard for cadastral mapping and parcel identification systems. This standard was revised in January 2012.
This standard provides recommendations on the development and maintenance of digital cadastral assessment maps, parcel data layers in a geographic information system, and parcel identifiers.[1]

IAAO is one of the standard making bodies for property assessment and valuation. The IAAO recognized the importance of parcel numbers across municipalities and developed a set of core recommendations for creating these PINs.

·       Compliance with Standards - The PIN should conform to defined standards including national, state and local standards.
·       Uniqueness – The most important aspect of the PIN is that it be unique.
·       Permanence – PINs should be permanent and only be changed in extreme circumstance.
·       Simplicity and Ease of Use – PINs should be as short as possible, uncomplicated, and easily understood.
·       Ease of Maintenance – The PIN should be easily maintained and accommodate changes such as a split or merge operation.
·       Flexibility – The PIN should also be flexible to accommodate not just land but multi-family dwellings, sub surface rights, leases, etc.

IAAO defines a parcel, a feature that is assigned a PIN, as a single, discrete piece of land having defined physical boundaries and capable of being separately conveyed.

In another national standards effort, Mortgage Industry Standards Maintenance Organization (MISMO)[2] has formed a working group to develop a national parcel identification system. MISMO was formerly a part of the Mortgage Electronic Registration Systems (MERS) and has recently been brought under the Mortgage Bankers Association (MBA).  The mortgage industry currently uses a combination of postal addresses, legal descriptions, assessor parcel numbers and geospatial coordinates to track homes. The MISMO Development Working Group (DWG) will focus on the development of universally accepted system parcel identification for the future mortgage market.

There is no universal standard for identifying a property, resulting in greater risk for mistakes and fraud. This proposed DWG seeks to bring together industry representatives to talk about current challenges, and possible enhancements for improving data standards in the realm of property location definition, verification and best practices. [3]

Another standard’s body is the Property Records Industry Association (PRIA), which was founded on the concept that government and business can work together to address issues of common concern in the world of property transactions.[4]  PRIA has established a GIS working group that has the following charge.

A recent estimate shows approximately 70% of all local governments have implemented some form of GIS.  Yet in many cases GIS is not integrated with the recording office. The PRIA GIS Workgroup has been chartered to establish standards, procedures and best practices for data exchange between GIS systems and land records systems. This will allow the exchange of information while taking into account performance, security, and revenue implications.

This group has not completed standards development but is working toward a national parcel identification system that will allow linkage between GIS features and source documents.

The FGDC Cadastral Data Content Standard and the core parcel publication guidelines derived from that standard also calls for a nationally unique parcel identifier.  In the case of the FGDC standard the national standard leaves the local parcel identifier in tact and appends the jurisdictions Federal Information Processing System (FIPS) code to the front of the local identifier.  The FIPS code assigned is determined from the supplying data steward.

The Open Standards Consortium for Real Estate (OSCRE) statement of purpose is “effective open standards are crucial for sharing information across boundaries and for systems that more easily interconnect.  Standards play a key role in innovation by giving businesses more choice in the software they use by reducing vendor lock-in and reduce the cost of IT by enabling a more competitive and diverse market.”[5]  OSCRE is a more international standards body than the others. In 2005 DoD adopted an agency wide real property unique identifier (RPUID) that was endorsed by OSCRE as a commercial best practice.[6]  The DoD’s RPUID is assigned to structures rather than land.  Every DoD building and structure is assigned a single number for its entire lifecycle. RPUIDs are tracked centrally in a registry and any authorized system in DoD can obtain information about a building by using the RPUID and web services to check the registry.

Each of the standards bodies has a slightly different need for a national identifier.  The activities and lessons learned from these standards organizations provide guidance on developing a parcel identification system.  One of the most important lessons seen throughout all of these standards organizations is to complete and unambiguous definitions of the feature being identified.    MISMO is focused on features that are identified in mortgage and loan documents, IAAO is focused on features that are assessed or taxed, PRIA is focused on connecting land descriptions to conveyance and other recorded documents, FGDC Cadastral Subcommittee is focused on maintaining the data steward’s identification number while allowing for national uniqueness, and OSCRE is focused on identifiers in the system architecture and business processes.  DoD’s implementation focused on buildings and structures.

Public Lands

None of the existing standards reviewed specifically address how public lands (non-taxable from a local government perspective) are assigned a parcel identifier and what defines the extent of the publically managed parcel.  In some areas of the public domain lands there are vast areas that have neither a survey nor a case transaction.  In these cases what is the best method for assigning a unique identifier to the land area that will define and relate to the land in a meaningful way and also be maintainable over time. Should every permit or transaction generate a new parcel identifier or should the parcel identifier be based only on the underlying land description and land survey? 

Two federal land management agencies, the Forest Service (FS) and the Fish and Wildland Service (FWS), currently use parcel identifiers.  In the FS system a master geodatabase is stored in a centralized location in Kansas City and is accessed through Citrix.  The updates are in real time using Oracle Spatial and the geodatabase is not versioned.  FS uses FME scripting to translate the production data into the publication data sets.  The enterprise data warehouse supports generating publication data and web-based services to support the decision support needs of the FS. The publication database is designed to support regular reporting needs such as the Land Area Report (LAR). The original FS withdrawal is assigned a parcel number and subsequent acquisitions or withdrawal actions are added with an assigned separate parcel identifier.  FWS does not maintain a BLM Case Serial number for acquisitions or withdrawals but does have a nationally internal unique parcel number for all parcels.  The original defined acquisition authorization area has a parcel identifier, as do all subsequent acquisitions with each conveyance or land ownership change assigned a new parcel identifier.  There was a large reconciliation project that worked through the FWS Lands database and the GIS to finalize and establish the unique parcel identifier across all systems.

In the Montana Cadastral System the publicly managed lands did not have a parcel identifier at the start because these lands were exempt from property tax systems.  But as the CAMA and GIS grew the need for an identifier for public lands (state, federal and county managed lands) became more apparent.  Attributes about the management agency and any actions on the lands had to be linked to the spatial feature in the GIS.  The publicly managed lands, including federally managed lands, are assigned a parcel identifier that is in part a geocode that identifies the county, the PLSS Township, section and if applicable, quarter section.  No parcel is larger than a section.  Federal lands smaller than a section are identified to either the quarter section and then further divisions according to the state DOR system for tagging areas smaller than a quarter section.

This system has worked well in Montana and although it is not synchronized with BLM records, as parcels are exchanged or apparent parcel configurations are changed, parcel identifiers are updated.  Montana recognized that the BLM often has a more granular definition of their land based on case actions.  Although desired, the state does not have a link to records in LR2000 that would facilitate a more complete representation of land transactions on federally managed lands in the Montana Cadastral System.

State Systems

Many state departments of revenue or taxation have some guidance on tax parcel identification; Florida, North Carolina, and Utah are three examples.  The state guidelines may or may not be enforced and there is significant variation in local governments even with state guidelines.  Utah’s state parcel identification guidelines provide three system or methods for parcel identification and summarizes these three commonly used systems.[7]

Proper identification of properties is essential to accurate valuation. A parcel identification system provides a method for referencing land parcels or data associated with parcels, using a number or code instead of a complete legal description.

It is important that the parcel numbering system allow the user to locate the parcel by means of the unique number. There are three kinds of numbering systems, which are suitable for this purpose.

In a map-base system, the first number sequence is assigned to a map, the second number sequence to a block or other organized map division, and the last to the individual parcel. An alternative map-base system is called a book-page system. The first number sequence is assigned to a book of maps, the second number sequence to a map page within the book, and the third to a parcel on the map.

Government Survey
The government survey takes for a base the existing land survey system of townships and ranges. The numbering sequences correlate with sections, quarter sections and other such subdivisions as necessary until the last number sequence, which refers to the individual parcel.

Geographic Coordinate Code (Geocode)
The geocode system is typically used on a computerized (GIS) system where the approximate center (paracentroid) of each parcel is identified. The parcel is numbered based on its x (east-west) location and y (north-south) location. Although the geocode system is accurate and quick, the parcel numbers do not tie directly to any given map or block. When a GIS mapping system is utilized, coordination with the AGRC is required to facilitate uniformity, data transfer, numbering schemes and formats used in parcel identification.

Local Systems

There are almost as many variations in local parcel identification systems as there are local systems.  Although the emergence of national CAMA vendors such as Thomson Reuters, Tyler Technologies, and Orion have reduced the number of local variations as these system each enforce consistent parcel identification requirements. It is not uncommon for a county to maintain several parcel identifiers with municipalities, the assessor, the treasurer and the planning agency each assigning a separate identifier. 

From a national perspective organizations that consume parcel data from many local jurisdictions especially across state lines are often confused about the formats and content of the parcel identifier.  While it is often possible to make each county’s parcel identifier unique by appending a local jurisdiction code to the front of the number, the structure of the parcel identifier, the content, special characters such as dashes or periods, and inconsistent usage such as the reuse of parcel numbers creates uncertainty when other data is connected to the local parcel data sets.  This typically happens with value added commercial data providers but can also occur in many other situations when the parcel data is used as base data for an application or to support a business need.


The basis for the identification number, whether it is computer generated or based on the parcel location or the parcel characteristics, was not found to be as critical for success, as the following.

(1)  The parcel being identified is well defined, recognized, and unambiguous.  For example are parcel identifiers attached to ownership parcels or to tax parcels?
(2)  The identification system, whether a number or intelligent key, must be unique across the entire system, never duplicated, and be easily generated.   
(3)  The parcel identification remains unchanged throughout the parcel’s life cycle, such as if the geometry of the parcel does not change than the parcel number should not change, and
(4)  The parcel identifier must be able to be used to link to related records and documents.

[2] MISMO®, the leading technology standards development body for the residential and commercial real estate finance industries, is a wholly owned subsidiary of the Mortgage Bankers Association. From last accessed 10-2-2012.
[5], last accessed 10-2-2012.
[6], last accessed 10-2-2012.

1 comment:

  1. There is a fairly comprehensive oil and gas focused tax parcel and surface ownership dataset at US Land Grid - - providing GIS tax ownership information for most oil and gas areas.