Grant County Commission holds work session 101221, part 4
By Mary Alice Murphy
[Editor's Note: The meeting went for a bit more than five hours, with a very short break. Several articles will cover the presentations and the review of the regular agenda, in addition to county and commissioner reports. Part 4 will cover the Grant County parcel mapping project update.]
Grant County commissioners heard from the contractor doing the parcel fabric project at their work session on Tuesday, Oct. 12, 2021.
The county contracted with Bohannon Huston engineering firm to do the parcel mapping project.
Krist Nelson of Bohannon Huston began the presentation using a PowerPoint graphical interface.
"I am a geospatial analyst," Nelson said. "The 17,000 subdivisions in Grant County have been adjusted to aerial accuracy. About 27,000 parcels will be adjusted to control. Bohannon Huston was tasked to create the parcel fabric. The county provided source data. We have provided training to the Grant County GIS (Geographic Information System) staff. Why a parcel fabric? Existing data was in some places highly inaccurate, off by as much as 200 feet. After the parcel fabric is completed, the maps will be much more accurate."
He showed a plat of the Rio Vicente subdivision, and then an aerial view of a portion of the map, with the parcel fabric overlaid. Nelson said the area had one of the largest inaccuracies, with the cul-de-sac not lining up accurately with the map and some boundary lines running through buildings. Using various steps in the process, he showed another image with the data matching up to the actual property boundaries. "With the way it lines up, we would believe that this data is much more accurate."
"A parcel fabric is a quilt of parcel data," Nelson explained.
The data includes dates, lines, lots, as well as data that is important to Grant County.
The production steps included starting with survey documents and reviewing 374 scans of subdivision plat documents. Bohannon Huston used survey techniques to make the plats digital. They then created the parcel lots and joined them to the parcel data that exists. They improved the accuracy by modifying parcels to control data, which is the aerial imagery. They then created the parcel fabric dataset.
During the analysis, they discovered that about 3,800 parcels needed to be adjusted. About 70 percent were "easy and automated split edits." The other 30 percent were more complex and required manual split edits. Some plats had the wrong rotational data applied, so that, too, has been corrected through rotation. Some parcels required a simple offset, with some needing both rotation and offset.
Part of Bohannon Huston's task going forward is to provide support and training for best practices to the GIS staff.
Nelson said the benefit of the parcel fabric data is that it is much more accurate, with 90 percent of it being with 9 feet of accuracy. "We have defendable accuracy with the parcel fabric, which now supports ongoing improvements. The cost has been about $6 per parcel of Phase 1."
He noted New Mexico Taxation and Revenue Department manages parcel data and holds that data. The department has encouraged counties to move to parcel fabric.
"We delivered Phase 1 on Aug. 20, 2021," Nelson said. "Phase 2 is about 80 percent complete for the control, and about 5 percent complete for adjustment of non-subdivided data. It will be about another four to six months for the final data to be completed."
District 5 Commissioner Harry Browne asked if Bohannon Huston had had to adjust sizes of parcels.
Nelson said there have been adjustments to the geometry of some parcels that were different from the stated acreage. "There has been some give and take done to the data."
Browne asked if there were any process for a landowner to have to pay or get compensation from the changes.
Nelson said any further legal identification would require another survey, even though it is based on survey data.
Dennis Sandine, the principal in charge of the project, said he understood the question to ask if the changes impact the landowner in any legal manner. "This parcel fabric is a legal document for NM Taxation and Revenue to allow the county assessor to assess the property. There is no legal impact to the property owner from the parcel fabric. It's just a representation. The survey document is the legal document for that parcel, which defines the exact area. The parcel fabric is to show, as accurately as possible, and to help the assessor assess the property and bring in accurate revenue to the county from taxes."
Browne asked if his understanding is that the taxes are based on inaccurate deed descriptions, but the legal records stored in the county are based on accurate parcel maps. Is that what you were saying?"
Sandine said: "No, I don't believe that is what I am saying. What we understand as surveyors, the surveyor creates a plat of a subdivision. The lots are taxed. But the survey itself may not be properly placed, so we have digitized the subdivision boundaries and placed them in the proper point in space. Compared to the previous data, we have improved the accuracy, improved the way the new acreage responds back to the survey data, so you're more closely aligned to the survey documents as compared to the existing data the county had. So, the survey documents are the legal representation of the land and that is what you would have to use in court. The parcel fabric has turned it into a digital format, which is more accurate."
District 4 Commissioner Billy Billings said the parcel map has just updated the information, but as he understands it, it has no legal bearing for people to look at. "No one's survey is going to change. No one's property value is going to change."
Assessor Raul Turrieta said during his past 30 years in the office, no one has contested the size of a property. It's for ad valorem tax purposes. "What they are doing is following what is done in the county."
Billings asked Bohannon Huston: "You are saying you can get within 9 feet. Is that as good as you can get? I was told by someone that other counties use a system where surveyors can get within 3 feet of accuracy."
Sandine said from what he has seen in imagery, "when we talk about 9 feet the national standard is within 9 feet. I picked 50 random points and visited each one. I tried to find the exact corners in the imagery. Of the 50, I could only identify 40. From imagery, it's very difficult to find the exact corners. The data, when it is put into the spreadsheet, identifies within 5 feet of the points I sampled. There is a 1.73 multiplier. The standard is to say that 95 percent of the data is within 9 feet. Parcel fabric allows survey point data to be put into the parcel fabric. If you start adding control data from field visits, you can likely improve the accuracy to less than 9 feet, even down to 3 feet. It is doable, but it would involve field surveys."
Nelson said some counties require subdivision plans to fit their control data. "They have control monuments in the field for the developer to tie their engineering documents to. That's how they control them. That will highly increase accuracy of new subdivisions that are platted."
The next presentation will address the 3 percent cap on property taxes.