(As a result of input from Nancy Von Meyer, (see below), I have revised some of the verbiage in this posting.)
During the next two weeks we will explore the Parcel Data Model used by the ESRI Parcel Fabric Land Records maintenance solution. This week we look into the polygon types that define the partitioning of lands into smaller divisions that can be sold and next week we will look at the polygon types that are used to store and maintain information on various forms of land ownership and obligation.
The Parcel Data Model used by the ESRI 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 Land Records.
Two Distinct Classes of Information
Overall, the data model breaks information into two distinct categories: 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 exhaustive, or even thorough. It is intended to be an introduction to the concepts and additional information can be found here.
Within each of these classes, information is split into discrete layers or "Types" of polygons.
The Partitioning classes are divided between Federal Subdivisions of Public Lands, commonly referred to as the Public Lands Survey System (PLSS) or Rectangular Survey System and Private Subdivisions in which private landowners divide their lands for sale to individuals.
Please note that I am purposely using the word "partitioning" instead of "subdivision" because there are so many meanings and implicit baggage that comes along when we use the word "subdivision". Recognize, the word "partition" is intended to define lands that are owned by an entity that is dividing up the lands so they may sell off portions of it to other individuals.
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. They 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.
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 he 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.
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.
Next Week: The Parcel Data Model - Ownership Types
Be sure to check back for our Blog Post next week in which we will continue our review of the Parcel Data Model and focus on the Ownership polygon "Types", (Tax Parcels, Owneship Parcels, Encumbrances, and Separated Rights.