Measurements versus Monuments

One of the more interesting effects of transitioning the way in which you manage your land records into the ESRI ArcGIS Parcel Editing Solution (the Parcel Fabric) is the transition from mapping parcels according to the measurements listed in the legal descriptions to mapping parcels according to the monuments called out in those legal descriptions.

Traditionally, and I am not sure whether this is the result of the limited data structures or just a misunderstanding into legal description interpretation, but, most mappers input the bearings and distances cited in the legal descriptions with little attention being paid to the accompanying monument calls.  You know.... "thence along the North right of way line" or "to the southeast corner of Lot 47" or "47.08 feet from the Northwest Section corner."

These calls, while they appear to be minor in nature, are actually more important that the actual measurements in the legal description.  For example, if a course is described as "thence North 26 degrees 15 minutes 26 seconds East, for a distance of 100 feet to the southeast corner of Lot 47", even if the actual bearing and distance to the southeast corner of Lot 47 is North 30 degrees East, a distance of 105 feet to the monument found located on the southeast corner of Lot 47, the property corner is the southeast corner of Lot 47 and the location of the monument supersedes the measurement called in the description and should be used for mapping.

These calls are commonly referred to as "monuments" and can exist in many forms: They can be natural monuments such as trees, streams, and lakes) or artificial monuments such as fences, walls, roads, streets or railroads. They can also be monuments described as the boundaries of adjacent parcels of land. The exact location of these monuments is considered "superior" to and carries a great deal of strength in determining the location of any specific corner, especially if that monument is called out in the legal description. 

Just a short note, for the monument call to be valid, it must be included in the legal description itself and cannot be inferred.

Monuments in the ArcGIS Parcel Editing Solution (the Parcel Fabric)

The Parcel Fabric is designed to enforce the manner in which the corner locations are defined, allowing the mapper to input the bearings and distances as cited in the description, but also locating the parcel corners on the existing mapped corners or "monuments".  This is accomplished using the "join" function inside the Parcel Fabric.  This "join" function allows the Parcel Fabric to locate a parcel corner so it is contiguous to and "along the right of way" or located at the "South East corner of Lot 47" or at "Section Corner" while maintaining the measurement information found in the source legal description.

This one function changes the way in which we handle the various inconsistencies contained in the legal descriptions, whether these inconsistencies are caused by differences in the precision of the measuring standards, differences in opinions of the locations of other monuments or improperly written deeds.  The "joining" functions allows us to analyze and map the "intent" of the description without being fixated on the measurements contained within. In my opinion, the one change is powerful and should be sufficient enough to convince us to begin managing our land records and parcel information in this new way.

I would be interested in hearing your views below.

The Parcel Data Model - The Partitioning Types

(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.

Partitioning Classes

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

The 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

Section Numbering and Sequence in which section lines are surveyed to subdivide Townships

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

Division of sections into 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

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). 

Private Partitions

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)

Private Subdivision

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)

Subdivision Lots and Tract

 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.