The Local Government Information Model and the Parcel Fabric
The Parcel Data Model used by the ESRI ArcGIS Parcel Editing Solution (the Parcel Fabric) is described in detail in the "GIS and Land Records" book by Nancy Von Meyer (ISBN-13: 978-1589480773). This data model provides the most comprehensive data structure focussed on Land Records we have seen to date and we highly recommend this data model to everyone involved in mapping Parcels and Land Records.
Two Distinct Classes of Information
Overall, the data model breaks information into two distinct groupings: the information that serves to partition lands (Public and Private) and the various types of land ownership (Tax Parcels, Fee Simple Ownership, Encumbrances and Separated Rights.)
The following discussion of Public and Private divisions is not intended to be thorough nor exhaustiveIt is intended to be an introduction to the concepts and additional information can be found here.
Within the Parcel Fabric, information is split into discrete layers or "Types" of polygons.
Federal Subdivisions of Public Lands
The polygon "Types" related to the Federal Partitions directly reflect the components of the Original Surveys from which the Federal lands were sold to private citizens through patents or deeds. These "Types" also reflect in many ways the order in which the lands are identified.
Type 1 - PLSS Townships
Type 1 polygons reflect the first division of Public lands from which all other divisions are derived. These "Townships", depending on the data of survey and instruction provided to the original surveyors may be anywhere from 6 miles square (the most common) to 7 miles square and several other variations. The "Townships" are identified by their sequence from the Initial Point in the Principal Meridian and are referenced in a North - South direction as lying North or South of the Base Line and East or West of the Principal Meridian.
All measurements involved in the PLSS are performed using the "Gunter's Chain", generally equivalent to 66 feet in length. The Gunter's "Chain" measures 66 feet long and consists of 100 "links", each link measuring approximately 7.92 feet.
Type 2 - PLSS Sections
Type 2 polygons reflect the second division of Public lands into smaller polygons approximately one mile by one mile in size. The sections are constructed after the Township perimeter has been established and monuments have been placed at defined locations by the original surveyor. They are numbered beginning with "one" at the Northeast corner of the Township and numbered sequentially in a snake pattern alternating east to west then southerly until all sections are identified. The "normal" section of land consists of approximately 640 acres.
Type 3 - Quarter Sections
Type 3 polygons reflect the third division of Public lands into smaller polygons by connecting straight lines between the monuments established by the original surveyor at the North, South, East and West lines of the sections. These are commonly referenced as "Quarter Sections".. The goal in establishing these quarter sections was to create as many aliquot portions of land containing as close to 160 acres of land as possible. If, however, the sections measured longer or shorter on the northern or western tiers of sections with the Township, smaller aliquot portions are created. These aliquot portions include the Government Lots around sovereign lands, previous land grants prior to the acquisition of the lands by the US Government or other situations.
There is a general misunderstanding of his process within the mapping community that believes that quarter sections are derived by dividing the Section into fourths - This is incorrect - The actual Sectional Breakdown process differs between Sections depending on the Section Number and where it is located in the Township.
Type 4 - Special Surveys
Type 4 polygons reflect the fourth division of Public lands and encompasses those situations in which special surveys were required. According to the BLM, these are non rectangular components of the PLSS including: Meandered Water, Corners and Conflicted Areas (known areas of gaps or overlaps between Townships or state boundaries).
The next two polygon "Types" describe the partitioning of lands by private landowners into smaller areas for sale to others. Because almost all lands in the United States are derived from the original public ownership managed by the Federal government, the exact location and definition of these private partitions (subdivisions) is completely dependent upon the quality of the location of the Public polygon types.
Type 5 - Simultaneous Conveyances (Subdivisions and Condominiums)
Type 5 polygons reflect the overall extent of privately owned lands that are partitioned into groups of smaller lots of units for sale. As with the smaller divisions of the Public lands partitions, the smaller units of the Private partitions come into existence at the moment that these partitions (Subdivision Plats or Declarations of Condominiums) are approved and recorded in the public records. In other words, the smaller divisions are "simultaneously" approved and "conveyed" into existence. Since these units are created at exactly the same time, none of these smaller units are "senior" nor "junior" to the rights of any other units in the subivision. These Type 5 polygons include those divisions commonly referred to as "Subdivisions" and "Condominiums".
Type 6 - Simultaneous Conveyance Divisions (Lots, Blocks and Units)
Type 6 polygons reflect the final type within the Parcel Data Model that reflects the partitioning of land for sale and does not contain any information about land ownership. This polygon type is intended to contain the smaller divisions of land with the larger Type 5 polygons (Simultaneous Conveyances). If the larger Type 5 polygon is a traditional Subdivision, these smaller divisions might be lots, tracts, reserved areas, road tracts or parks. If the Type 5 polygons is a Condominium, these polygons may represent the individual unit boundaries, including its 3D space, limited common ownership, or general common ownership.
The remaining polygon types within the Parcel Data Model cover the various ways in which land can be owned. The following discussion is not intended to be a treatise on land ownership in the United States, but a generalized discussion of how these ownerships are stored with the Parcel Data Model.
Ownership interests within the United States are not a single right, but are often referred to as a "Bundle of Rights." As such, one can possess a a majority of the rights (this is often referred to as "fee simple ownership", or a single temporary or permanent right.
Type 7 - Right to Pay Taxes - Tax Parcels
The first ownership type stored in the Parcel Data Model is intended to store and manage information about the "right to pay taxes". This is the polygon type most often mapped and maintained by Property Appraisers (Assessors) offices through the country. One general misconception by the general public equates these parcels to "ownership" of the parcels, without realizing these polygons represent the tax obligation, or those properties on which ad valorum taxes are paid and may not represent true ownership. This is especially true where there are long term lease interests that contractually have been obligated to pay the taxes on this lands under lease (think shopping malls, etc.)
Type 8 - Fee Simple Ownership - Ownership Parcels
The second ownership type, and the eighth polygon type in the Parcel Data Model is intended to store and manage Fee Simple Ownership. Specifically, this is often used to map and maintain surface rights and neither subsurface rights such as minerals or gas nor air space rights. While most agencies at the moment do not maintain information on these ownerships, I envision a time when it will become increasingly important.
Type 9 - Less than Fee Simple Ownership - Encumbrances
The next ownership type is that of Encumbrances. Black's Law defines encumbrances as the right of use over the property by another. In this sense, any use of the property by anyone other than the fee simple landowner can be considered an encumbrance. Encumbrances are often limitations of the use of the land by the fee simple owner. Various types of encumbrances include: rights of way or road easements, drainage or flowage easements, conservation easements, fishing easements, grazing rights or utility easements.
Type 10 - Separated Rights
The next ownership type is that of Separated Rights. As noted in the Cadastral Data Content Standard for the National Spatial Data Infrastructure: separated rights are rights and interests in land ownership that can be disconnected from the primary or fee simple surface ownership. For example, mineral and oil rights are often separated from the surface ownership.
Type 11 - Other Rights
The final polygon type is intended to cover those other ownership interests that do not fit into any of the other polygon types.