Whether a parcel map is created for an engineering project, land development, valuation, tax assessment, land administration and management, for a subdivision, city, county, or whole country, the tools to create and manage them have dramatically improved.

In the past, a key sticking point for surveyors was the lack of solid COGO tools within legacy GIS. “There are still workflows for parcel creation that might involve importing the geometry from CAD or scanning a map, but you can also do the COGO directly in ArcGIS Pro when adding parcels to the Parcel Fabric,” said Tim Hodson, principal product engineer at Esri. “You can do grid-to-ground corrections, etc., and ellipsoid-based directions are also supported, such as true mean bearing, rhumb line, and forward geodetic.”

Curves had always been a point of contention. For a while, many GIS folks referred to a variety of geometric elements generically as “arcs,” though not necessarily referring to defined circular arcs (e.g., C3, C5, PC Pt, etc.). “Arcs” were often roughly segmented for display purposes (even CAD does this in its own way). The difference now is that the arc definitions in Esri geodatabases are stored parametrically for circular arcs, elliptical arcs, clothoid spirals, and for Bezier curves. (See graphic.)

Adjustments can be needed for the process of surveying land boundaries. Few things sent surveyors into a tizzy in the early days of GIS like the term “rubber sheeting.” No, the adjustment tools in Parcel Fabric are not anything of that sort. The adjustment engine is DynAdjust (pro.arcgis.com/en/pro-app/latest/help/data/parcel-editing/least-squares-parcel-fabric.htm), a relatively new program born, and collaborated on in the GitHub era, taking advantage of advances in processing and computing, e.g., Intel’s Math Kernel Library (MKL). Everyone has their favorite least squares adjustment tool. But with DynAdjust built in, you do not have to go through extra exports and imports.

There is an associated XML format that makes the import of survey data from many platforms easy. DynAdjust might be unfamiliar to many in the surveying community, but it is worth a look; read this FIG paper: Click Here 

There’s flexibility in what to do with the results of say, a least-squares adjustment. You might not want to or be authorized to update the parcel. For example, it might represent a tax parcel geometry of record. You can store the adjustment linework as another class. It may inform a future update of other parcel classes or be awaiting QA/QC steps.

Another key improvement is in how controlling points and boundary courses are handled. “You can configure the attributes of points and courses. We have out-of-the-box attributes for what we refer to as fixed points,” said Hodson. “They can be held in adjustments, and if an editor tries to move it, a constraint prevents this—you get a pop-up error message.” This is what surveyors are used to in their surveying software.

Another key consideration for wide area mapping that surveyors are keenly aware of, is the difference between “grid” and “ground.” Maps are projected to conform to the shape of the particular area of the earth they cover, as closely as possible. However, not close enough to match a distance physically measured on the ground (considering factors including the curvature of the earth), and distances of record. For a recorded survey, the “ground” distances can be labeled. But how can you do this for thousands of parcels?

Hodson’s paper explains:

“Mapped lines representing boundaries are stored as line features in the parcel fabric. Using distances as an example, the legally documented value for a specific boundary line is stored as an attribute on the feature. The geometry shape length is also stored as a separate property of the line feature. The shape property is dynamic and is designed to be allowed to change by user workflows; it is system maintained. By comparison, the stored record distance value may only be changed directly by the user and is never automatically changed by the system. It is changed by a user if, for example, a mistake is found, and the value needs to be explicitly updated to match the legal record.”

If you want to add more information and categorize points based on other characteristics, you can do this by adding new attribute fields. For instance, you might wish to assign confidence levels to points from different sources. This can enable different weighting strategies. Linda M. Foster, PLS, GISP, MGIS director, land records/cadastre solutions at Esri said that there is an out-of-the-box schema, but that you can easily extend the schema to include various types of attribute rules and constraints.

“It’s a very flexible model, but starts with a standard foundation,” said Foster. “Once you get to know the schema and system, you can modify and augment—without having to do code-level customization.”

What Foster points out is a key contrast between the tools of yesteryear and today. GIS and geospatial practitioners in the past had to be experts in their respective fields, and a mix of IT specialist, coder, and data scientist. Now, you can be a subject matter expert, without the software being as much of a burden.

Who’s Parcel Mapping?

In North America, as well as in other parts of the world, the driver for map creation is taxation. County tax assessor maps, even though some are very rough precision-wise, were a foundational element of nearly all early GIS.  The same with early road/street features. Often, new layers were built off these early streets and parcel layers, inheriting imprecision. Despite this, the value of these layers has been tremendous. Parcel Fabric can be a tool to update and improve legacy layers.

There is substantial value in parcel maps for spatial analysis, correlation with economic data, developing zoning strategies, insurance rates, public safety, and much more. For state and federal agencies, land management and administration of public lands would be cumbersome to impractical without a parcel base.  

There are many countries that have cadastres, one of the earliest was established under Napoleon. They vary, depending on how they serve as a registry of titles and deeds, and in what order of how the act of registration occurs and what happens when there are changes in ownership. That subject would take a multi-volume book series to fully explore, but here are some examples.

The Netherlands cadastre is managed by a public agency called “Kadaster” (kadaster.nl/about-us), which manages the land registry and the associate property rights. Kadaster has an international group, which helps developing countries develop their own cadastres. In some cases, these new cadastres are the mechanism by which land tenures have been formalized and delivered to individuals for the first time.

Nealy every country in the EU has some form of cadastre. They vary in what role each plays as an instrument for land registry and ownership. Sweden, for example, has what many refer to as a coordinate-based cadastre. It is also unique in that all property surveys are conducted by the national mapping agency (lantmateriet.se/en/) and/or local municipalities.

In some countries, a land surveyor need not be licensed for most types of surveying work, however, to submit or update any survey data for the official cadastre, there are very stringent education, experience, and examination requirements. Foster said that British Columbia, Canada, has a cadastre, though not necessarily as the sole instrument of land administration. Similarly, the City of Calgary has a modernized parcel mapping initiative underway. Esri is working with a team in South Australia (where the Torrens Title system had been pioneered in the mid-1800s) on an updated cadastre. 

In the U.S., a cadastre as an official instrument for land title, ownership, and conveyances does not exist. However, there are parcel bases for nearly every state, county, and municipality. Except where a state’s laws clearly require that a licensed land surveyor be the creator, or oversee the creation of a parcel base, they can be created and maintained by non-surveyors. However, in many cases, surveyors are tapped for parcel mapping. After all, if you want to create a geology layer, wouldn’t you want a geologist involved?

If I could offer an amalgam of experiences GIS managers have shared on this subject of who should be parcel mapping: “In the early days we got surveyors involved, but they wanted to do a lot of field surveying, and that got too expensive. Plus, they would not compromise on precision. We had to build the parcel map in a hurry with a small budget. Now, we’re getting surveyors involved to improve the parcel layers”.

Transforming Challenges into Opportunities

One issue with parcel layers is, no matter how large you put disclaimers, unwitting misuse will occur. I’m sure that many county parcel map managers have had folks call up asking why their hand-held recreational GPS does not line up with the parcel lines on the map (and also cuts through their garage). The imprecise compounded by the imprecise. People are becoming more aware of this, and easily accessible consumer applications, like turn-by-turn navigation, are helping. They learn in real-world situations that both the GPS and the map source have a lot of inherent fuzz. 

Foster also noted a county in California that is updating its parcel base, with the full capabilities of Parcel Fabric, and that this is being overseen by licensed surveyors.

“Among the many goals for this modernized parcel theme is digital submission,” said Foster. “For instance, a private surveyor submitting a subdivision plat to the county for review. That’s where things are really moving into the future, with digital delivery.” Another great example of a large parcel base is Harris County Texas (Houston and the surrounding area), and its online parcel viewer: arcweb.hcad.org/parcelviewer.

An updated, precise, and data-rich parcel layer is imperative for any initiative seeking to create digital twin cities. Even if that is not the driver, the era of fuzzy parcel layers (hopefully) will soon be in the past. For whatever reason you may seek to create a parcel map, the resources and tools have never been better. 

Sidebar:

A Large Agency Implementation

The U.S. Bureau of Land Management (BLM) utilizes the Esri ArcGIS Pro Parcel Fabric for the production, maintenance, and dissemination of the Public Land Survey System (PLSS) dataset. The BLM identified this software as being well suited for the diverse requirements of the BLM Cadastral Group. The PLSS dataset serves as the vision for the National Spatial Data Infrastructure (NSDI) and the National Cadastre within the NSDI is to have a single source of authoritative cadastral data that is controlled and managed by designated data stewards. 

To effectively manage land data, the BLM required a survey-based land management software that integrates survey records and associates this information with the corresponding geospatial features. Parcel Fabric features an extendable database design, which includes essential point and line attributes that facilitate Coordinate Geometry (COGO) data entry, encompassing bearings, distances, and support for curved line entries. Furthermore, the incorporation of a weighted least-squares engine enables the adjustment of data in accordance with established best practices. 

The BLM found Parcel Fabric’s built-in tools valuable for enhancing data quality management. The tools BLM found useful include standard topology rules, data validation layers, and the capability to implement attribution rules. The automation of data integrity maintenance has been a priority for the BLM. 

Another recent advancement for the BLM has been the implementation of an ArcGIS Pro Enterprise Deployment. This development allows for a multi-editor solution that enables the simultaneous management of non-PLSS datasets, while ensuring that the geometry of the PLSS is maintained within a single parcel fabric database. 

Read Part 1 Here

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