An End to the Pin Farm
August 30, 2006
About 20 years ago, when surveyors of the city of Huntsville, Ala., keyed in subdivisions via plat or legal description based only on estimated section corners, a subdivision could be as much as 50 ft off from its true location in any or all directions. Every department in the city worked off different base maps, different scales and different compilation years back then. There was no consistent data.
Project after project was hampered by the inability to get accurate coordinates of Public Land Survey System (PLSS) corners, a requirement in Huntsville. While the city used GPS coordinates to georeference base maps and for ground control of the city's mapping projects beginning in 1987, the grid of coordinates did nothing to help document the coordinates for section corners. Positional accuracy for the maps took a giant leap forward but the section corners remained elusive. GPS usage for locating section corners would have been a nice solution as well, but GPS was new and expensive so the practicality of locating section corners and documenting their coordinates was nothing more than a pipedream at that time. We desperately needed a solution.
Correcting SubsTo improve our processes on subdivision jobs, we first standardized the city's base maps by producing large scale topographic maps, then built GIS data on top of it, including data related to sanitary sewers, storm sewers, zoning, city limits, wetlands, soils and geology information. The project then matured into a fairly complex set of databases, including online interactive mapping. We then began serving it over a local network, allowing everyone to utilize the same GPS-controlled map.
But when subdivision plats were entered into the GIS based on the PLSS, there were frequent errors, all related to differences in where the elusive section corners were. The section corners in the field did not match the positions that were scaled off on the maps.
An economical solution for this problem, established in 1994, was to require state plane coordinates on all points defining the boundary of a subdivision. The coordinates were to be based on the GPS monuments since traditional surveys were still the norm. This eliminated the error of tying to a section corner (for legal purposes, the tie to the public survey was still included in the new requirements) and provided a good fit to the base maps. This solved the problem for our subdivision plats, and Huntsville was given a national achievement award for the regulations requiring state plane coordinates.
The Program ProposedWhile Huntsville's dilemma regarding subdivisions was solved, the section corner problems were not. Like any city, Huntsville is swimming in legal documents. Many of them describe boundaries that need to be input into the city's GIS databases. GIS analysts are constantly tasked with keying in legal descriptions of land parcels, rights of way, easements, zoning lines and other data. Each description starts from the ever-elusive section corner. Naturally, the descriptions seldom fit without a lot of manipulation, which costs money and time, and often causes great frustration.
The most recent struggle with section corners came in the form of a Letter Of Map Revision, or LOMAR. LOMARs are a product of the Federal Emergency Management Agency (FEMA) and are a way of certifying that a subdivision or parcel has been removed from a floodplain. Developers will often purchase land in a floodplain, fill it above the established flood elevation and submit data to FEMA to have it removed from the floodplain. This eliminates the need for flood certificates and flood insurance for would-be buyers. Like other documents, the land removed from the floodplain is delineated by a legal description tied to those ever-elusive section corners.
On one particular LOMAR produced in September 2005, the boundary described did not match the fill pad shown on the city's maps. Lots shown on the developer's plans as being high and dry were still showing low and wet according to the LOMAR description. After some investigation, the cause was apparent. The section corner referenced in the field was almost 80 ft away from the section corner in the base maps. The needed fix would require additional work and timely delays. Arguments began between the developer and the city. Eventually a solution was agreed upon, but the delays and arguments could have been avoided if all were able to agree on where the section corner actually was.
"This has got to stop," I thought. Then a light bulb came on. Gone are the days when GPS was expensive and sparsely available. These days, the technology is used by numerous surveyors. I realized that local surveyors are already collecting section corner data in their everyday activities. The city just needed to create a clearinghouse for that information for everyone to use.
Thus began the makings of the Section Corner Identification (SCID) program. In the summer of 2005, I approached the local surveyor's chapter, the Tennessee Valley Professional Land Surveyors Society, and proposed a fix to the problems associated with section corners: the acquisition of coordinates on the corners. The plan would work as follows, I explained:
- Local surveyors would occupy purported section corners or quarter section corners with GPS units during their normal business routines. n They would voluntarily submit the coordinates to the city of Huntsville GIS division.
- The GIS division would publish the coordinates on an Internet site for everyone to use.
- The GIS division would also agree to move the base map corners to the coordinates provided by the local surveyors.
The chapter agreed to the proposal and SCID was born.
Development of a Solid ProgramOver a period of time everyone could potentially use the same point for a section corner, eradicating the errors in legal description starting points. This would positively affect easements, minor subdivision plats, rights of way, zoning lines, annexations and other land parcels with a tie to the PLSS. The SCID program could also have the potential to stop another common problem with the PLSS known as the multiple corner, pin farm or pincushion effect. This is where many pins are driven into the ground in and around an area purported to be a section corner-a place where one surveyor refuses to hold the existing monument because he believes his 1/100 ft difference is more correct, thus deserving another pin. The rules developed for the SCID program state that only one coordinate will be published.
After the ground rules were established, Erin Dyer, a GIS analyst, and Thomas McDonough, a GIS programmer/analyst with the city of Huntsville GIS division, began creating a web page of section corner identification data. Once a working model of the page was operational in March, section corner coordinates began to pour in. The Madison County Survey Department, for one, became an enthusiastic supporter of SCID. "It's something I've wanted for years," says Shelby Aston, head of the survey department. His crews have documented more than 250 corners so far. Many of the Tennessee society chapter members said it would serve as an example to be used at the state level, since the state has discussed similar projects but has not been able to successfully implement them.
Another proponent of the system, Jerry D. McCarley, PLS, vice president of Garver Engineering LLC in Huntsville, beams, "the SCID program is an excellent program to preserve and protect the corners that remain."
By July's end, the database contained more than 320 published section corner coordinates and continues to grow. Also, the city of Huntsville is happy to have recorded 10 ancillary points that are not section corners but points that local surveyors have expressed merit in for preserving their locations.
The Huntsville SCID is an example of a program that not only solves technical problems in the often unseen world of government regulations but also brings public and private sectors together to solve problems within our local community. The historic preservation of section corners, the increased accuracy in mapping and the problems solved by having common coordinates produces multiple benefits for the professionals involved in the area's projects and every citizen within our city.
The Huntsville, Ala., interactive online mapping portal can be found at http://gismaps.hsvcity.com.
Sidebar: SCID RulesThe following rules have been established for the submittal of corners through the SCID:
- Corner information must be submitted only by surveyors licensed in the state of Alabama. No blind submittals will be accepted.
- GPS occupation of the corner is preferred, although in some cases traditional surveys combined with GPS occupation will be accepted.
- GPS occupations and traditional surveys should be performed in compliance with The Standards of Practice for Surveying in the State of Alabama.
- All submittals are voluntary and subject to publication.
- Data may be submitted online or in hard copy to The City of Huntsville Geographic Information Systems Division.
- Data submitted will not be a direct entry into the database. It will be reviewed and published by the GIS staff.
- Submittals for the same corner will be published on a first-come basis.
- Only section corners and section quarter corners will be accepted.
- Disputes over corner coordinates shall be submitted to The City of Huntsville GIS Division for review.
- To avoid duplication of database records, all coordinates will be published as the northwest corner.