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. 

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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

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

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

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

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

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

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. 

What is the Parcel Fabric?

By now, most GIS professionals interested in maintaining Land Records in GIS have heard of the ESRI Parcel Fabric but, considering the adoption rate I've been witnessing, many are still reluctant to fully adopt the concept and implementation. Many of you have heard me speak in the past few years about the benefits and challenges involved in moving your data to the Parcel Fabric. Future posts will discuss options for implementing the Parcel Fabric, but in this post, I will attempt something a little less challenging and introduce the various components of the Parcel Fabric.

Conceptual Data Model - The Design

Within the Parcel Fabric, features are defined by the "type" of polygon they represent. For example there are:  Legal definitions of how land is divided such as the Public Land Survey System Townships, Sections, Quarter Section, Special Surveys, or by the legal subdivisions of the land such as subdivisions or condominiums and the interior subdivisions inside these legal entities (lots), or they are defined by "types" of interests in the land such as: taxable interests, ownership interests and other partial interests such as easements or leasehold interests. By far, this approach is the most comprehensive attempt to map all components of land interests in decades and the initial concept can be found in GIS and Land Records by Nancy von Meyers of Fairview Industries. This approach provides a logical place for all types of interests in land and tracks how the land is defined and ownership of interests in that land.

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Logical Data Model - The Way it Works in ArcGIS

The Parcel Fabric is a complete land records data model that consists of several standard feature classes in a geodatabase that are "tied together" similar to a geometric network. When I first introduce the structure to my students, I almost always describe the Parcel Fabric as a "geometric network for polygons."

As a matter of fact, the entire Parcel Fabric data model revolves around the polygon as the primary geometry with all other information being related to that polygon geometry. This is very different from the cartographic data model that many organizations are still using where everything revolves around lines.

The Parcel Fabric data model, and specifically the Local Government Information Model, provides the polygon feature class as the primary record and then has corresponding lines that define that polygon and corners that define how those lines are joined to one another.  It also includes a table to store information about the document that created the polygon (the plan table) and a feature class to store control points that define the spatial locations of the points relative to the surface of the Earth.

 Local Government Information Model (LGIM) - The Standardization

The Local Government Information Model is ESRI's attempt to develop and promote a standardized data model to allow greater consistency across organizations sharing similar needs, but also having that standardized data model adopted to allow the development of enhanced and complex maintenance functions that make Land Records maintenance more efficient.  In other words, by having everyone, or at least those organizations seeking more efficiency, adopt the LGIM, ESRI can develop sophisticated tools that allow us to perform standard maintenance tasks in fewer steps with fewer mistakes.

Tools - Let's Make it Easier

While I plan on having many posts directly relating to specifics of the Tools available for the Parcel Fabric, I can say that, with each new release of ArcGIS for Desktop, ESRI continues to improve the quality of the parcel editing tools, making them more and more efficient and making the job of the Parcel Mapper easier.

For example, some of the new tools included in the Parcel Editor functions in ArcGIS for Desktop can do things such as: take an existing parcel polygon, calculate a portion of that "parent" parcel, calculate and input all lines required for that portion and the parent parcel, store and create two new parcels and mark the existing parcel historic so we can go back and see what the parcel looked like before we performed that split. ESRI has also integrated these tools into Automated Parcel Editing Workflows that will identify and guide you through step involved in parcel maintenance.  These workflows are a great first step in making the software easier to use and, while still needing refinement, you can see the commitment of ESRI towards building a complete solution for Parcel Maintenance. 

These tools are only available once you adopt and implement the Parcel Fabric as your parcel maintenance solution. The LGIM and the enhanced parcel maintenance tools go hand in hand and make the maintenance of land records better.

Hopefully this short post helps with your understanding of the Parcel Fabric, or maybe just piqued your interest to learn more.  If you have questions or comments, please share them below.

Is the Parcel Fabric worth the squeeze?

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"Is the Juice worth the squeeze?" is one of my favorite expressions - it so clearly focuses the decisions we make, especially relating to technology. I am reminded of this today as I was discussing with two of our clients whether to remap their parcels in the Parcel Fabric for parcel maintenance purposes.

By far, the greatest challenge with the Parcel Fabric is transitioning from your current data model into the highly structured Local Government Information Model. 

You may currently be using a "cartographic" data model in which you use lines and pieces of text to convey information about the features contained on your map. While this model is great if your primary focus is in producing that map, it does not provide a complete picture as far as this elements on which you wish to store information.  For example, you may only store lines showing where the extent of lots differ from the extent of tax parcels, or you may store pieces of text to convey dimensions instead of actually storing the information as an attribute of the lines.  While not trivial, these deficiencies can be overcome for the transition into the Parcel Fabric.

Or, you may have issues with topology.  Storing features in separate feature classes, or "layers" often leads to having features that do not "line up" with features in other layers. While not difficult to correct, especially with the many topology tools in ArcGIS, the process is often time consuming and tedious.  Be warned, this MUST be corrected prior to transition into the Parcel Fabric. While there are procedures for correcting these issues in the  Parcel Fabric, it is far easier to only import features that align with each other.

Finally, you may find you have issues with the spatial location of your features. While there are many ways to correct the spatial location in the Parcel Fabric, including moving the features, and least squares adjustments, since features in the Parcel Fabric are interconnected, when you move one feature, it will change any connected feature.

I am a licensed Surveyor in several states who has been involved in GIS for over three decades and, without a doubt, the Parcel Fabric is the best data model we have seen for the storage and maintenance of land records. The Parcel Fabric is the first data model that allows us to keep and maintain essential information about a particular parcel within the model.  What is the document that created, modified or defined this parcel? Is there a digital copy of that document available for viewing? What are the dimensions of the boundary as shown on the originating document? What are the mapped dimensions? What rotation or scaling had to be performed to make the parcel fit? Are there differing boundary dimensions for the adjoining parcels? What are the lines associated with a specific parcel? These are just a few of the questions that the Parcel Fabric allows us to answer.

We plan on discussing in an upcoming post the advantages of the Parcel Fabric, but, for now, understand that, while the data model is a great incentive for transitioning, the maintenance of your land records is the main reason to consider moving into the Parcel Fabric.

While not perfect, the tools that ESRI has built for the Parcel Editor continue to get better and better with each new release. I am amazed by the fact that a single tool can perform in one step as many as five separate steps required when editing features that are stored with corresponding topology rules. Granted, you must take the time to learn and understand these new tools to truly become efficient with the procedures, but, as with all things in life, this efficiency comes with time and experience.

We provide parcel maintenance services for many counties and, after transitioning all of these counties into the Parcel Fabric, we find that the time we spend on the actual maintenance of the data is greatly reduced, more controlled and reproducible, and we are better able to document and track the results of this maintenance. As a matter of fact, we have seen reductions of the time it takes to perform this maintenance of up to 50%.  That, my friends, is the main reason to consider, and transition your parcel data into the Parcel Fabric.

The Parcel Fabric is worth the squeeze.

Welcome

Welcome to the first major redesign of the Panda Consulting website in close to ten years.  With this redesign, we hope to be able to better communicate with you and more readily share our ideas and findings with you.

In addition to restructuring the web content and using a template that is "adaptive" in nature to whatever type of device you are using to consume this content, we are also beginning a blog on which we will share our findings, thoughts and insights.

We plan on beginning a series of blogs directly related to the ESRI Parcel Fabric, its structure, problems and resolutions you might use during the conversion of your existing data into the Parcel Fabric, and insights into the best practices for integrating the Parcel Fabric into your organization.

We have been using the Parcel Fabric now for several years and helped dozens of clients make this transition and discovered what works and what still needs some work and, hopefully, you will find something in these posts to help you on your journey.

Let's get started.